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Análise dos mecanismos resistentes e das similaridades de efeitos da adição de fibras de aço na resistência e na ductilidade à punção de lajes-cogumelo e ao cisalhamento de vigas de concreto.; Analysis of resistant mechanisms and similarities of the addition effect of steel fibers on strength and ductility to both the punching shear of flat slabs and the shear of concrete beams.

Holanda, Kristiane Mattar Accetti
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 02/10/2002 PT
Relevância na Pesquisa
36.72%
Um dos principais problemas das lajes-cogumelo refere-se à ruína por puncionamento da ligação laje-pilar. Esta forma de ruína deve ser evitada, proporcionando-se às lajes as melhores condições para o desenvolvimento de mecanismos de escoamento das armaduras e de ruína por flexão, antes da ocorrência da ruína por cisalhamento. A introdução de fibras de aço em elementos de concreto submetidos a solicitações tangenciais proporciona melhoria de desempenho, seja pelo aumento da capacidade resistente, seja pela alteração da forma de ruína. Pretende-se contribuir com o avanço do conhecimento sobre o assunto, explorando aspectos como a análise das similaridades dos efeitos da adição de fibras de aço na resistência e na ductilidade de lajes-cogumelo à punção, com aqueles que se observam no cisalhamento de vigas prismáticas análogas. Abordam-se os casos de ligações laje-pilar interno sem armadura de punção, variando-se a resistência do concreto, a taxa e o tipo de fibra utilizado. A partir dos resultados experimentais, verificou-se que existe uma similaridade de comportamento estrutural entre esses dois elementos e concluiu-se que é possível utilizar ensaios de cisalhamento em vigas prismáticas para se obter indicadores a serem utilizados nos ensaios de punção de lajes. Foi efetuada uma análise da adaptabilidade de modelos teóricos existentes sobre cisalhamento em vigas e punção em lajes...

"Distribuição de tensões em testes de cisalhamento e micro-cisalhamento mediante análise de elementos finitos" ; A finite element stress analysis of shear and micro-shear bond strength tests

Placido, Eliane
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 23/06/2006 PT
Relevância na Pesquisa
36.71%
Os objetivos deste estudo foram comparar, através de análise de elementos finitos, a distribuição de tensões em modelos que representam arranjos experimentais nor-malmente utilizados em testes de cisalhamento e micro-cisalhamento, verificar a tendência de variar o local de início e o modo de fratura em função de mudanças nos parâmetros dos ensaios e analisar a influência de dois modos de fixação do substrato sobre a concentração de tensões. Os modelos bidimensionais em estado plano de deformações representaram o compósito (híbrido ou flow) aderido à dentina através de uma camada de adesivo de 50 μm. Duas condições de fixação da dentina foram estabelecidas: na primeira (mais rígida), os deslocamentos foram restritos em todas as direções nos nós das arestas que representam as três superfícies livres de adesão e na segunda, a restrição foi colocada apenas na parte posterior da dentina. Foi aplicado um carregamento pontual a várias distâncias da interface dentina-adesivo, de modo a obter um tensão nominal constante de 4MPa. Foram analisadas as tensões máximas de tração e cisalhamento, a distribuição das tensões ao longo dos nós da interface dentina-adesivo e os vetores de tensão máxima principal...

Análise comparativa entre modelos de predição de norma e dados de ensaios na determinação da resistência ao cisalhamento.; Comparative analysis among standards prediction models and tests data in shear strength determination.

Hirata, Fernando Pessoto
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 05/06/2013 PT
Relevância na Pesquisa
36.71%
Desde o início do século XX, com as publicações de Ritter e Mörsch, o fenômeno da resistência ao cisalhamento de elementos em concreto armado começou a ser intensamente estudado. Diversos modelos de cálculo foram criados, tentando predizer o valor da resistência ultima de elementos de concreto armado, quando solicitados por esforços cisalhantes. O fenômeno da resistência ao cisalhamento é extremamente complexo, sendo influenciado por diversos fatores. A elaboração de ensaios e modelos de predição se torna complexa, pois, determinar quais são os parâmetros que influenciam significativamente o fenômeno do cisalhamento, não é simples. Outras dificuldades são: relacionar a resistência ao cisalhamento com o grau de solicitação por esforços fletores e compreender em quais intervalos de parâmetros os principais fatores influenciam o fenômeno. Sendo assim, é essencial verificar a aplicabilidade das normas técnicas em diversos intervalos destes fatores ou parâmetros. A partir da coleta de cerca de 1.200 resultados de ensaios de laboratório de vigas de concreto armado, solicitadas por esforços de cisalhamento, elaborou-se um banco de dados com os resultados de ensaios da força última resistente, juntamente com diversos parâmetros de cada ensaio. Para analisar os valores de predição das normas e os valores dos resultados de ensaios...

Investigação geofísica e resistência ao cisalhamento de resíduos sólidos urbanos de diferentes idades; Geophysical investigation and shear strength of municipal solid wastes with different landfilling ages

Abreu, Ana Elisa Silva 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 08/05/2015 PT
Relevância na Pesquisa
36.72%
Este trabalho apresenta a caracterização in situ de propriedades de interesse geotécnico de maciços de resíduos sólidos urbanos (RSU) e o estudo das propriedades de resistência ao cisalhamento de RSU com diferentes idades. Foram realizadas investigações por sondagens e com métodos geofísicos sísmicos no Aterro Sanitário de São Carlos (ASSC) e ensaios de cisalhamento direto de grandes dimensões (50x50 cm2) com amostras de diferentes idades de aterramento coletadas no ASSC, no Lixão Desativado de São Carlos e em Aterro Experimental construído nas proximidades do Lixão. As investigações realizadas no ASSC revelaram que as diferentes fases de operação do maciço (aterro controlado e aterro sanitário) produziram dois estratos com diferentes propriedades geotécnicas. A umidade, as velocidades de propagação de ondas sísmicas e o peso específico in situ dos dois estratos são distintos, sendo sempre menores e menos dispersos no estrato mais raso (operado como aterro sanitário) e maiores e mais dispersos no estrato mais profundo (operado como aterro controlado). Realizaram-se tentativas de determinação do peso específico in situ dos RSU com medição dos volumes escavados por substituição de volume. Notou-se que os furos tendiam a diminuir de diâmetro assim que a composição de sondagem era retirada e que o método adotado para avanço dos furos...

Desenvolvimento de equipamento Ring Shear para avaliação do comportamento de solos a grandes deformações

Santos, Viviane Rocha dos
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
36.72%
Os movimentos de massa de solo, geralmente, estão relacionados com a mobilização da resistência de uma ou várias superfícies de ruptura pré-existentes. Dessa maneira, o conhecimento da propriedade que rege esse comportamento (resistência ao cisalhamento residual) é de extrema importância no estudo da estabilidade de solos. Segundo Skempton (1985), resistência ao cisalhamento residual é a resistência mínima constante que o solo pode atingir, a baixas taxas de cisalhamento, após sofrer grandes deslocamentos. A determinação dos parâmetros de resistência ao cisalhamento residual pode ser realizada através de ensaios de cisalhamento por torção do tipo ring shear, adequado para estudar os mecanismos atuantes na ruptura, uma vez que permite a continuidade dos deslocamentos no solo. Nesse contexto, a pesquisa teve por objetivo desenvolver um equipamento de cisalhamento torsional baseado no ring shear descrito por Bishop et al. (1971) para avaliar o comportamento do solo a grandes deformações. O equipamento projetado foi validado, preliminarmente, segundo os resultados já publicados na literatura.; Landslides, generally, are related with the mobilization of shear strength of one or more preexisting rupture surfaces. Thus...

Effect of fiber orientation on the shear behavior of glass fiber/epoxy composites

Almeida, Jose Humberto S.; Angrizani, Clarissa C.; Botelho, Edson C.; Amico, Sandro C.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 789-795
ENG
Relevância na Pesquisa
36.72%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); This paper deals with the study of the influence of the lay-up configuration on interlaminar and in-plane shear properties of glass fiber reinforced epoxy composites. The following laminates were produced by resin transfer molding with vacuum assistance for this study: [0](5), [90](5), [0/90/0/90/0] and randomly oriented (mat). The composites, with similar overall fiber volume fraction, were evaluated based on four tests: double-notched shear, short beam shear, V-notched rail and Iosipescu shear tests. Besides, the dynamic shear modulus was measured with non-destructive testing based on free vibration method. The [0](5) laminate presented interlaminar shear strength almost twice that of [90](5), whereas the mat samples presented higher in-plane shear strength in both tests used due to its random fiber orientation. The dynamic shear modulus was higher for the composites [0](5), as expected due to the longitudinally oriented fibers. Among the shear test methods applied, double-notched and V-notched methods exhibited more auspicious features...

One-dimensional viscoelastic fluid model where viscosity and normal stress coeffients depend on the shear rate

Carapau, Fernando
Fonte: F. Carapau, "One-dimensional viscoelastic fluid model where viscosity and normal stress coeffients depend on the shear rate",Nonlinear Analysis:Real World Applications, Volume 11, Issue 5, pp. 4342-4354, 2010. Publicador: F. Carapau, "One-dimensional viscoelastic fluid model where viscosity and normal stress coeffients depend on the shear rate",Nonlinear Analysis:Real World Applications, Volume 11, Issue 5, pp. 4342-4354, 2010.
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
46.6%
Westudy the unsteady motion of a viscoelastic fluid modeled by a second-order fluid where normal stress coefficients and viscosity depend on the shear rate by using a power-law model. To study this problem, we use the one-dimensional nine-director Cosserat theory approach which reduces the exact three-dimensional equations to a system depending only on time and on a single spatial variable. Integrating the equation of conservation of linear momentum over the tube cross-section, with the velocity field approximated by the Cosserat theory, we obtain a one-dimensional system. The velocity field approximation satisfies both the incompressibility condition and the kinematic boundary condition exactly. From this one-dimensional system we obtain the relationship between average pressure and volume flow rate over a finite section of the tube with constant and variable radius. Also, we obtain the correspondent equation for the wall shear stress which enters directly in the formulation as a dependent variable. Attention is focused on some numerical simulation of unsteady/steady flows for average pressure, wall shear stress and on the analysis of perturbed flows.

Nonlinear Shear and Extensional Flow Dynamics of Wormlike Surfactant Solutions

Yesilata, B.; Clasen, Christian; McKinley, Gareth H.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Pré-impressão Formato: 890751 bytes; application/pdf
EN_US
Relevância na Pesquisa
36.72%
Nonlinear shear and extensional flow dynamics of rheological properties of a wormlike micellar solution based on erucyl bis (2-hydroxyethyl) methyl ammonium chloride, EHAC, are reported here. The influences of surfactant (EHAC) and salt (NH4Cl) concentrations on the linear viscoelastic parameters are determined using small amplitude oscillatory shear experiments. The steady and time-dependent shear rheology is determined in a double gap Couette cell, and transient extensional flow measurements are performed in a Capillary Breakup Extensional Rheometer (CABER). In the nonlinear shear flow experiments, the micellar fluid samples show strong hysteretic behavior upon increasing and decreasing the imposed shear stress due to the development of shear-banding instabilities. The non-monotone flow curves of stress vs. shear rate can be successfully modeled in a macroscopic sense by using the single-mode Giesekus constitutive equation. The temporal evolution of the flow structure of the surfactant solutions in the Couette flow geometry is analyzed by instantaneous shear-rate measurements for various values of controlled shear-stress, along with FFT analysis. The results indicate that the steady flow bifurcates to a global time-dependent state as soon as the shear banding/hysteresis regime is reached. Increasing the salt/surfactant ratio or the temperature is found to stabilize the flow...

Quantitative ultrasound imaging during shear wave propagation for application related to breast cancer diagnosis

Alavi Dorcheh, Marzieh
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
EN
Relevância na Pesquisa
36.72%
Dans le contexte de la caractérisation des tissus mammaires, on peut se demander ce que l’examen d’un attribut en échographie quantitative (« quantitative ultrasound » - QUS) d’un milieu diffusant (tel un tissu biologique mou) pendant la propagation d’une onde de cisaillement ajoute à son pouvoir discriminant. Ce travail présente une étude du comportement variable temporel de trois paramètres statistiques (l’intensité moyenne, le paramètre de structure et le paramètre de regroupement des diffuseurs) d’un modèle général pour l’enveloppe écho de l’onde ultrasonore rétrodiffusée (c.-à-d., la K-distribution homodyne) sous la propagation des ondes de cisaillement. Des ondes de cisaillement transitoires ont été générés en utilisant la mèthode d’ imagerie de cisaillement supersonique ( «supersonic shear imaging » - SSI) dans trois fantômes in-vitro macroscopiquement homogènes imitant le sein avec des propriétés mécaniques différentes, et deux fantômes ex-vivo hétérogénes avec tumeurs de souris incluses dans un milieu environnant d’agargélatine. Une comparaison de l’étendue des trois paramètres de la K-distribution homodyne avec et sans propagation d’ondes de cisaillement a montré que les paramètres étaient significativement (p < 0...

A generic mechanics approach for predicting shear strength of reinforced concrete beams.

Zhang, Tao
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2014
Relevância na Pesquisa
36.77%
This thesis includes a series of journal articles in which a mechanics based segmental approach is developed for simulating shear behaviour of reinforced concrete (RC) beams. Using the well-established theories of partial interaction and shear friction, the generic mechanics approach simulates the formation and widening of diagonal cracks and shear sliding failure for RC beams. Being mechanics based, the proposed approach can be generally applied to various kinds of structures, that is any cross section, with any type of concrete and reinforcement and with any bond properties. Moreover, no component of the proposed approach relies on empiricism to account for the mechanics of shear failure, and the approach can accommodate any material characteristics which with time can be refined and revisited to improve the accuracy of shear strength simulation. In developing the mechanics of the segmental approach for prestressed RC beams, it is shown how the approach is applied to analyse shear behaviour and simulate shear failure of prestressed beams. Parametric studies are conducted to explain the effect of prestress on shear behaviour. For verification, the proposed approach is applied to 102 specimens and the analytical and experimental results are in good agreement. The generic nature of the mechanics approach is shown by its application to steel and fibre-reinforced polymer (FRP) reinforced beams and one-way slabs without stirrups. From the mechanics of the segmental approach...

Quantifying the compressive ductility of concrete in RC members through shear friction mechanics.

Chen, Yongjian
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2015
Relevância na Pesquisa
36.73%
This thesis contains a series of journal papers in which the compressive ductility of concrete in RC members has been quantified through shear friction mechanics. Firstly, the size dependent stress‐strain models for unconfined and actively confined concrete are derived based on the fundamental mechanics of shear friction theory. At this stage, the shear friction properties, that is the relationship between the shear stress, normal stress, crack widening and interface slip across the sliding plane, are not specifically required. It is shown how the stress‐strain from cylinder tests of one specific length can be modified to determine that for any size of cylinder. Moreover, it is shown that the proposed approach can be used to make existing generic stress/axial‐strain relationships size dependent and these size dependent relationships can be directly used to determine the corresponding size dependent stress/lateral‐strain relationship. Being mechanics based, size dependent stress‐strain models reduce the reliance on vast experimental testing as only one size of specimen needs be tested to obtain stress‐strain relationships for all sizes. Secondly, the shear friction properties, that is the relationship between the shear stress...

Desenvolvimento de ferramentas e provetes para o ensaio Thick Adherend Shear Test (TAST).

Morais, João Francisco Alves
Fonte: Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto. Publicador: Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto.
Tipo: Dissertação de Mestrado
Publicado em //2013 POR
Relevância na Pesquisa
36.75%
As estruturas coladas são geralmente projetadas para que o adesivo seja essencialmente sujeito a esforços de corte, pois neste tipo de solicitação o adesivo apresenta melhores caraterísticas mecânicas. A avaliação do comportamento ao corte pode ser realizada com o adesivo no estado maciço ou como camada fina em juntas adesivas. Os métodos que permitem avaliar o comportamento ao corte, quer para o adesivo, quer para as juntas, são: o ensaio Iosipescu ou V-Notched beam shear method, o ensaio de borboleta ou Notched plate shear method (Arcan), o ensaio de torsão, o ensaio de tração numa junta de sobreposição simples e o ensaio Thick Adherend Shear Test (TAST). Os ensaios Arcan e Iosipescu, tal como o ensaio de torção, podem ser realizados em provetes de adesivo maciço ou em juntas. O ensaio de torção é pouco utilizado, porque a aplicação do esforço de corte exige dispositivos e equipamentos de ensaios complexos. Os ensaios Arcan e Iosipescu utilizam provetes com entalhes e podem introduzir alguma dificuldade na medição precisa das deformações. O ensaio de tração numa junta de sobreposição simples é um dos métodos mais usados para caraterizar uma junta adesiva, porque é um método simples, as juntas são de fácil fabrico e pode ser realizado em máquinas universais de ensaios mecânicos. Neste ensaio os aderentes estão sujeitos a uma solicitação de tração...

CFRP SHEAR STRENGTHENING OF REINFORCED CONCRETE T-BEAMS WITH CORRODED SHEAR LINKS

Qin, Shunde; Dirar, Samir; Yang, Jian; Chan, Andrew H. C.; Elshafie, Mohammed
Fonte: American Society of Civil Engineers Publicador: American Society of Civil Engineers
Tipo: Article; accepted version
EN
Relevância na Pesquisa
36.73%
This is the author accepted manuscript. The final version is available from American Society of Civil Engineers via http://dx.doi.org/10.1061/(ASCE)CC.1943-5614.0000548; This paper investigates the structural behavior of uncorroded as well as corroded RC T-beams strengthened in shear with either externally bonded (EB) carbon fiber?reinforced polymer (CFRP) sheets or embedded CFRP rods. Nine tests were carried out on RC T-beams having an effective depth of 295 mm and a shear span to effective depth ratio of 3.05. The investigated parameters are the shear link corrosion level (uncorroded, 7% corroded, or 12% corroded) and type of CFRP strengthening system (EB CFRP sheets or embedded CFRP rods). The unstrengthened beams with shear link corrosion levels of 7 and 12% had shear strengths that were 11 and 14%, respectively, less than the shear strength of the uncorroded unstrengthened beam. Both the embedded CFRP rods and EB CFRP sheets were effective in enhancing the shear strength of tested beams but the effectiveness of both strengthening systems decreased with increasing shear link corrosion level. The shear strength enhancement provided by the embedded CFRP rods and EB CFRP sheets decreased from 19 and 15%, respectively, to 12 and 11%...

Acoustic Radiation Force Impulse-Driven Shear Wave Velocimetry in Cardiac Tissue

Bouchard, Richard Robert
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2010
Relevância na Pesquisa
36.73%

Acoustic radiation force impulses (ARFI) have been used to generated transverse-traveling mechanical waves in various biological tissues. The velocity of these waves is related to a medium's stiffness and thus can offer useful diagnostic information. Consequently, shear wave velocimetry has the potential to investigate cardiac disease states that manifest themselves as changes in tissue stiffness (e.g., ischemia).

The work contained herein focuses on employing ARFI-based shear wave velocimetry techniques, similar to those previously utilized on other organs (e.g., breast, liver), for the investigation of cardiac tissue. To this end, ARFI excitations were used to generate slow-moving (under 3 m/s) mechanical waves in exposed myocardium (with access granted through a thoracotomy); these waves were then tracked with ultrasonic methods. Imaging techniques to increase frame-rate, decrease transducer/tissue heating, and reduce the effects of physiological motion were developed. These techniques, along with two shear wave velocimetry methods (i.e., the Lateral Time-to-Peak and Radon sum transformation algorithms), were utilized to successfully track shear wave propagation through the mid-myocardial layer in vitro and in vivo. In vitro experiments focused on the investigation of a shear wave anisotropy through the myocardium. This experimentation suggests a moderate shear wave velocity anisotropy through regions of the mid-myocardial layer. In vivo experiments focused on shear wave anisotropy (which tend to corroborate the aforementioned in vitro results)...

The Adaptive Response of Endothelial Cells to Shear Stress Alteration

Zhang, Ji
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2010
Relevância na Pesquisa
36.76%

The adaptive response of vascular endothelial cells to shear stress alteration induced by global hemodynamic changes is an essential component of normal endothelial physiology in vivo; and an understanding of the transient regulation of endothelial phenotype during adaptation will advance our understanding of endothelial biology and yield new insights into the mechanism of atherogenesis. The objective of this study was to characterize the adaptive response of arterial endothelial cells to acute increases in shear stress magnitude and frequency in well-defined in vitro settings. Porcine endothelial cells were preconditioned by a basal level shear stress of ±15dynes/cm^2 at 1 Hz for 24 hours, and an acute increase in shear stress magnitude (30 ±15 dynes/cm^2) or frequency (2 Hz) was then applied. Endothelial permeability to bovine serum albumin was measured and gene expression profiling was performed using microarrays at multiple time points during a period of 6 hours after the shear stress alteration. The instantaneous endothelial permeability was found to increase rapidly in response to the acute increase in shear stress magnitude. Endothelial permeability nearly doubled after 40 minutes exposure to the elevated shear magnitude...

Shear Wave Imaging using Acoustic Radiation Force

Wang, Michael Haizhou
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2013
Relevância na Pesquisa
36.72%

Tissue stiffness can be an indicator of various types of ailments. However, no standard diagnostic imaging modality has the capability to depict the stiffness of tissue. To overcome this deficiency, various elasticity imaging methods have been proposed over the past 20 years. A promising technique for elasticity imaging is acoustic radiation force impulse (ARFI) based shear wave imaging. Spatially localized acoustic radiation force excitation is applied impulsively to generate shear waves in tissue and its stiffness is quantified by measuring the shear wave speed (SWS).

The aim of this thesis is to contribute to both the clinical application of ARFI shear wave imaging and its technical development using the latest advancements in ultrasound imaging capabilities.

To achieve the first of these two goals, a pilot imaging study was conducted to evaluate the suitability of ARFI shear wave imaging for the assessment of liver fibrosis using a rodent model of the disease. The stiffness of severely fibrotic rat livers were found to be significantly higher than healthy livers. In addition, liver stiffness was correlated with fibrosis as quantified using collagen content.

Based on these findings, an imaging study was conducted on patients undergoing liver biopsy at the Duke University Medical Center. A robust SWS estimation algorithm was implemented to deal with noisy patient shear wave data using the random sample consensus (RANSAC) approach. RANSAC estimated liver stiffness was found to be higher in severely fibrotic and cirrhotic livers...

Enhancement of fluid permeability during shear deformation of a synthetic mud

Zhang, Shuqing; Cox, Stephen
Fonte: Royal Asiatic Society Publicador: Royal Asiatic Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.74%
This study concerns the effect of stress paths on permeability and permeability anisotropy in a synthetic mud at conditions where cataclastic flow is dominant. The synthetic mud is composed of 10 wt.% montmorillonite, 40 wt.% illite, and 50 wt.% silt-sized quartz. In the experiments where the mud was first consolidated at 90 MPa effective pressure (pe) and then also sheared at 90 MPa pe, permeability decreased continuously with increasing shear displacement; subsequent shear deformation at 30 MPa and 20 MPa effective pressure resulted in permeability increases. The permeabilities parallel to and across the mud layer are similar during shear deformation at 90 MPa pe and remain so during shear deformation at lower pe. In the experiments where shear deformation commenced at 30 MPa pe after an initial consolidation at 90 MPa, permeability increased significantly with increasing displacement. Combined effects of reducing mean effective stress and shear sliding result in permeability enhancement up to two orders of magnitude. The permeability parallel to the shear direction is one order of magnitude higher than that across the shear plane. Our shear deformation experiments at high pressures confirm the importance of stress path on the evolution of fluid permeability during shear deformation. The experimental results clearly indicate that to effectively enhance permeability and to channel fluids along shear zones in wet sediments...

Geochemical variations and element transfer during shear-zone development and related episyenites at middle crust depths: insights from the Mont Blanc granite (French-Italian Alps)

Rossi, M; Rolland, Y; Vidal, O; Cox, Stephen
Fonte: Geological Society of London Publicador: Geological Society of London
Tipo: Parte de Livro
Relevância na Pesquisa
36.72%
This paper highlights the relationships between the formation of shear zones, associated quartz-rich veins and their quartz-depleted alteration haloes ('episyenites') that have formed in the Mont Blanc Massif during the Alpine orogeny. The shear zones are steeply dipping and formed late (18-13 Ma) during collisional orogeny, at mid-crustal depths (5 ± 1 kbar, 400 ± 50 °C) during uplift of the Mont Blanc Massif. Between the shear zones, nearly undeformed granite contains widely dispersed, subhorizontal veins with a quartz-dominant quartz + albite + chlorite + adularia assemblage. They do not intersect the shear zones and are surrounded by quartz-depleted alteration haloes up to several metres wide. The compositions of the shear zones and the vein-alteration haloes (episyenites) show substantial departures from the bulk composition of the host rock. Shear zones are characterized by greenschist facies assemblages (epidote-, chlorite- or K-white-mica-bearing assemblages). Each shear zone type is featured by a specific chemical change: depletions in K2O, and enrichments in Fe2O3 and CaO (epidote-); with depletions in CaO, Na2O, K2O and slight SiO2 enrichments (white mica-chlorite-); with depletions in SiO2, CaO, Na2O, K2O and enrichments in MgO (phlogopite-chlorite shear zones). Episyenites are characterized by chemically induced porosity enhancement due to dissolution of magmatic quartz and biotite...

Evidence for shear heating, Musgrave Block, central Australia

Camacho, A; McDougall, Ian; Armstrong, Richard; Braun, Jean
Fonte: Pergamon-Elsevier Ltd Publicador: Pergamon-Elsevier Ltd
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.72%
The phenomenon of shear-heating is generally difficult to recognise from petrologic evidence alone. Establishing that shear zones attain higher temperatures than the surrounding country rocks requires independent evidence for temperature gradients. In the Musgrave Block, central Australia, there is a clear spatial association between shear zones and interpreted elevated temperatures. Eclogite facies shear zones that formed at ~ 550 Ma record temperatures of ~650-700°C. Outside the high-pressure shear zones, minerals with low closure temperatures such as biotite (~450°C in the 40Ar-39Ar and Rb-Sr systems), preserve ages >800 Ma, suggesting that these rocks did not experience temperatures greater than about 450°C at ~550 Ma for any extended period. Thus, the shear zones record temperatures that are ~200°C higher than the surrounding country rocks. Simple calculations show that the combination of relatively high shear stresses (~100 MPa) and high strain rates (~10-11 s-1) for short durations (<1 Ma) can account for the observed apparent temperature variations. The evidence indicates that shear heating is the dominant mechanism for localised temperature increases in the shear zones, while the country rock remained at relatively lower temperatures.

Fan-structure shear rupture mechanism as a source of shear rupture rockbursts

Tarasov,B.G.
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2014 EN
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This paper proposes the further development of a recently identified shear rupture mechanism (fan mechanism) that elucidates a paradoxical feature of hard rocks - the possibility of shear rupture propagation through a highly confined intact rock mass at shear stresses that can be significantly less than frictional strength. In the fan mechanism, failure is associated with consecutive creation of small slabs (known as 'domino blocks') from the intact rock in the rupture tip, driven by a fan-shaped domino structure representing the rupture head. The fan head combines such unique features as extremely low shear resistance, self-sustaining stress intensification, and self-unbalancing conditions. Consequently, the failure process caused by the mechanism is inevitably spontaneous and violent. Physical and mathematical models explain unique and paradoxical features of the mechanism, which can be generated in primary ruptures and segmented faults. The fan mechanism provides a novel point of view for understanding the nature of spontaneous failure processes, including shear rupture rockbursts. The process explains, in particular, features of shear rupture rockbursts such as activation at great depths, generation of new shear ruptures in intact rock mass...