The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Thomas A Taylor - One of the best experts on this subject based on the ideXlab platform.
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Thermal fracture of ceramic thermal barrier coatings under high heat flux with Time-Dependent Behavior.: Part 1. Experimental results
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: B.d. Choules, Klod Kokini, Thomas A TaylorAbstract:Abstract The objective of this research was to study the thermal fracture of ceramic thermal barrier coatings under high heat flux laser heating and investigate the effect of Time-Dependent Behavior of the ceramic. Continuously plasma-sprayed zirconia coatings with thicknesses varying from 0.26 to 1.5 mm were heated with a CO 2 laser to maximum surface temperatures varying from 700 to 1700°C. Temperature differences from 600 to 1300°C across the ceramic coating were applied. High heat flux heating was found to cause changes in the material, leading to a denser microstructure and relaxation of compressive stresses. These changes lead to the development of surface and interface cracks during ambient air cooling following laser heating. Increasing the coating thickness was found to decrease the number of surface cracks developed and increase the distance between cracks. Surface cracks were found to extend further into thin coatings than thick coatings. Increasing the maximum surface temperature was found to increase the surface crack length. The thinnest and thickest coatings developed fewer and shorter interface cracks than coatings with intermediate thicknesses.
Klod Kokini - One of the best experts on this subject based on the ideXlab platform.
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Time-Dependent Behavior and Fracture of Functionally Graded Thermal Barrier Coatings under Thermal Shock
Materials Science Forum, 2005Co-Authors: Klod Kokini, Sudarshan RangarajAbstract:The thermal fracture and its dependence on Time-Dependent Behavior in functionally graded yttria stabilized zirconia - NiCoCrAlY bond coat alloy thermal barrier coatings was studied. The response of three coating architectures of similar thermal resistance to laser thermal shock tests was considered, experimentally and computationally.
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Thermal fracture of ceramic thermal barrier coatings under high heat flux with Time-Dependent Behavior.: Part 1. Experimental results
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: B.d. Choules, Klod Kokini, Thomas A TaylorAbstract:Abstract The objective of this research was to study the thermal fracture of ceramic thermal barrier coatings under high heat flux laser heating and investigate the effect of Time-Dependent Behavior of the ceramic. Continuously plasma-sprayed zirconia coatings with thicknesses varying from 0.26 to 1.5 mm were heated with a CO 2 laser to maximum surface temperatures varying from 700 to 1700°C. Temperature differences from 600 to 1300°C across the ceramic coating were applied. High heat flux heating was found to cause changes in the material, leading to a denser microstructure and relaxation of compressive stresses. These changes lead to the development of surface and interface cracks during ambient air cooling following laser heating. Increasing the coating thickness was found to decrease the number of surface cracks developed and increase the distance between cracks. Surface cracks were found to extend further into thin coatings than thick coatings. Increasing the maximum surface temperature was found to increase the surface crack length. The thinnest and thickest coatings developed fewer and shorter interface cracks than coatings with intermediate thicknesses.
B.d. Choules - One of the best experts on this subject based on the ideXlab platform.
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Thermal fracture of ceramic thermal barrier coatings under high heat flux with Time-Dependent Behavior.: Part 1. Experimental results
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: B.d. Choules, Klod Kokini, Thomas A TaylorAbstract:Abstract The objective of this research was to study the thermal fracture of ceramic thermal barrier coatings under high heat flux laser heating and investigate the effect of Time-Dependent Behavior of the ceramic. Continuously plasma-sprayed zirconia coatings with thicknesses varying from 0.26 to 1.5 mm were heated with a CO 2 laser to maximum surface temperatures varying from 700 to 1700°C. Temperature differences from 600 to 1300°C across the ceramic coating were applied. High heat flux heating was found to cause changes in the material, leading to a denser microstructure and relaxation of compressive stresses. These changes lead to the development of surface and interface cracks during ambient air cooling following laser heating. Increasing the coating thickness was found to decrease the number of surface cracks developed and increase the distance between cracks. Surface cracks were found to extend further into thin coatings than thick coatings. Increasing the maximum surface temperature was found to increase the surface crack length. The thinnest and thickest coatings developed fewer and shorter interface cracks than coatings with intermediate thicknesses.
Jian-fu Shao - One of the best experts on this subject based on the ideXlab platform.
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A micro-macro model for Time-Dependent Behavior of clayey rocks due to anisotropic propagation of microcracks
International Journal of Plasticity, 2015Co-Authors: Christian Bikong, Dashnor Hoxha, Jian-fu ShaoAbstract:In this paper, a micro-macro model is proposed for the Time-Dependent Behavior of clayey rocks. Two material scales are considered. At the mesoscopic scale, the studied material is represented by a three-phase composite. Quartz and calcite grains are embedded inside the clay matrix. At the microscopic scale, the clay matrix is characterized by a cracked elastic solid. The creep deformation is assumed to be induced by the Time-Dependent propagation of anisotropic microcracks inside the clay matrix. A two-step homogenization procedure is proposed. The effective elastic properties of the cracked clay matrix are first determined using an Eshelby solution based homogenization method. Two different homogenization schemes are used respectively with and without taking into account crack interactions. Then the macroscopic mechanical properties of heterogeneous clayey rocks are determined by the second homogenization step using the Mori Tanaka Scheme. A sensitivity study is performed in order to evaluate macroscopic consequences of the microscopic Time-Dependent propagation law of microcracks. Finally, comparisons between numerical results and experimental data from creep tests are presented.
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Multi-scale modeling of Time-Dependent Behavior of claystones with a viscoplastic compressible porous matrix
Mechanics of Materials, 2014Co-Authors: Yun Huang, Wanqing Shen, Jian-fu Shao, Ariane Abou-chakra Guéry, Yun JiaAbstract:This paper is devoted to multi-scale modeling of Time-Dependent Behavior of claystones using a two-step homogenization procedure. Two materials scales are considered. At the mesoscopic scale, the material is constituted by a clay matrix and embedded mineral grains. At the microscopic scale, the clay matrix is a porous medium composed of a solid phase and spherical pores. The macroscopic plastic criterion of the clay matrix is first determined by a modified secant method (Maghous et al., 2009) considering a pressure sensitive yield function for the solid phase. This criterion is then used as the loading function for the description of viscoplastic deformation of the clay matrix, together with a non-associated viscoplastic potential. At the second step of homogenization, the macroscopic Behavior of the claystone is determined by taking into account the effect of mineral grains (quartz and calcite). For this purpose, we propose an extension of the incremental approach initially proposed by (Hill, 1965) to modeling of Time-Dependent Behavior. Therefore, the micromechanical model is able to explicitly account for the effects of pores and mineral grains at two different scales. The numerical algorithm for numerical implementation of the micromechanical model is also presented. The proposed model is finally verified through comparisons between numerical results and experimental data in triaxial compression tests with constant strain rate and in triaxial creep tests.
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A Micromechanical Model for Time Dependent Behavior Related to Subcritical Damage in Quasi Brittle Rocks
Springer Series in Geomechanics and Geoengineering, 2013Co-Authors: Yaoying Huang, Jian-fu ShaoAbstract:In France, an underground research laboratory is constructed in a clay formation, called Callovo-Oxfordian argillites. In order to evaluate quantitatively the structure durability, it is necessary to achieve a good understanding of the long-term Behavior of the material. Subcritical crack growth is one of main causes of Time-Dependent Behavior in rock. In order to rigorous modeling of the Time-Dependent Behavior of studied material, a micromechanical model incorporated subcritical damage propagation is proposed for Callovo-Oxfordian argillites in this paper. In the proposed constitutive model, the argillite is considered as a two phase composite: the clay matrix and the mineral inclusion. Based on experimental observations [1], the clay matrix is described by a Time-Dependent damage model and the mineral inclusions are described by a linear elastic model. The passage from the micro-scale to the macro-scale is done through different homogenization schemes for studying their influences on the subcritical propagation of cracks.
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A multiscale modeling of damage and Time-Dependent Behavior of cohesive rocks
International Journal for Numerical and Analytical Methods in Geomechanics, 2009Co-Authors: Ariane Abou-chakra Guéry, Jian-fu Shao, Fabrice Cormery, Djimedo KondoAbstract:The present paper deals with a micromechanical approach to modeling the Time-Dependent mechanical Behavior of a class of cohesive geomaterials. The considered material is Callovo-Oxfordian argillite, which is mainly composed of three constituents: an elastoviscoplastic clay matrix, elastic quartz minerals, and elastic damaged calcite grains. The macroscopic constitutive law is obtained by adapting the incremental method proposed by Hill (J. Mech. Phys. Solids 1965; 13:89-101). Its unified formulation allows a description of not only the Time-Dependent Behavior of the argillite but also its elastoplastic damage response. The developed model is first validated by comparison with finite element solutions and then it is applied to the prediction of argillites' macroscopic responses in connection with their mineralogical compositions. The validity of the model is checked through comparisons between the model's predictions and experimental data.
G G Whelan - One of the best experts on this subject based on the ideXlab platform.
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Time-Dependent Behavior in a transport-barrier model for the quasi-single helcity state
Plasma Physics and Controlled Fusion, 2014Co-Authors: P W Terry, G G WhelanAbstract:Time-Dependent Behavior that follows from a recent theory of the quasi-single-helicity (QSH) state of the reversed field pinch is considered. The theory (Kim and Terry 2012 Phys. Plasmas 19 122304) treats QSH as a core fluctuation structure tied to a tearing mode of the same helicity, and shows that strong magnetic and velocity shears in the structure suppress the nonlinear interaction with other fluctuations. By summing the multiple helicity fluctuation energies over wavenumber, we reduce the theory to a predator?prey model. The suppression of the nonlinear interaction is governed by the single helicity energy, which, for fixed radial structure, controls the magnetic and velocity shearing rates. It is also controlled by plasma current which, in the theory, sets the shearing threshold for suppression. The model shows a limit cycle oscillation in which the system toggles between QSH and multiple helicity states, with the single helicity phase becoming increasingly long-lived relative to the multiple helicity phase as plasma current increases.
