The Experts below are selected from a list of 228 Experts worldwide ranked by ideXlab platform
Pouyan Shen - One of the best experts on this subject based on the ideXlab platform.
-
pulsed laser ablation synthesis of magnesiowustite based phases with special defect clusters Interfaces and internal stress implications for natural occurrence and engineering applications
CrystEngComm, 2015Co-Authors: Tsungyi Lin, Shihsiang Lin, Shueiyuan Chen, Pouyan ShenAbstract:Nanocondensates of rocksalt-type (R) magnesiowustite and minor spinel-type (S) magnesioferrite with paracrystalline distribution of defect clusters were fabricated by pulsed laser ablation of MgO–Fe2O3 solid solution (9 : 1 molar ratio) under specified power densities in air and characterized by X-ray/electron diffraction and optical absorption spectroscopy. The predominant magnesiowustite nanocondensates have well-developed {100}, {110}, {111} facets for (hkl)-specific coalescence as unity and bicrystal with exact/almost {110} 70.5° twist boundary, {111} twin boundary, (1)/(001) heteroInterface, and (100)R/(310)S Interphase Interface constrained by [01]R//[001]S. The magnesiowustite nanocondensates have a minimum band gap of ca. 3 eV for potential opto-electronic catalytic applications and a significant internal compressive stress of ca. 2.5 GPa when fabricated at a relatively high power density, shedding light on its natural high-pressure occurrence.
-
Oxidation–decomposition facilitated reorientation of nanoparticles in reactively sintered (Ni0.33Co0.67)1−δO polycrystals
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: Ming-yen Li, Pouyan Shen, Shyh-lung HwangAbstract:Abstract (Ni 0.33 Co 0.67 ) 1− δ O polycrystals with rock salt structure and a bimodal size distribution due to reactive sintering at 1000 °C were subject to annealing at 720 °C for 2–72 h in air and studied by analytical electron microscopy with regard to the effect of oxidation decomposition on the reorientation of nanoparticles in host grains. Upon annealing, the nanoparticles rapidly oxidized as spinel structure progressively Co-richer, whereas the host protoxide grains with rock salt-type structure progressively Ni-richer. The spinel particles less than 100 nm in size readily detached from grain boundaries and fell into parallel epitaxial relationship with respect to the host protoxide grains sharing a coherent Interface. Such a Brownian-type reorientation process, in terms of anchorage release at Interphase Interface and driven by epitaxy energy cusp, at a rather low apparent homologous temperature ( T / T m =0.45) was facilitated by oxidation decomposition process and nanometer-size effect.
-
Reorientation of intra- and intergranular particles in sintered Y-PSZ/Co1−xO composites
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: Wen-hsu Lee, Pouyan ShenAbstract:Abstract Yttria-partially stabilized zirconia (Y-PSZ)/Co1−xO composites 1:99 in molar ratio were sintered and then annealed at 1600 °C for 1–100 h in air to produce reorientation of the embedded particles. Transmission electron microscopy (TEM) of all samples indicated the submicron, but not larger, Y-PSZ particles fell into parallel epitaxial orientation with respect to the host Co1−xO grain sharing preferred {111} Interface and {100} ledges. Brownian-type rotation of the embedded particles in terms of anchorage release at the Interphase Interface is indicated by this and our previously studied case of opposite (Y-PSZ)/Co1−xO composites with Co1−xO as the embedded particles. In the present case, however, detachment or bypassing of Co1−xO grain boundaries in the early firing stage already caused significant orientation as well as shape changes of intergranular Y-PSZ particles.
Louisette Priester - One of the best experts on this subject based on the ideXlab platform.
-
Interaction of lattice dislocations with the α-γ Interphase Interface in a stainless steel bicrystal
Philosophical Magazine A, 2002Co-Authors: A. Taisne, B. Decamps, Louisette PriesterAbstract:Abstract The elementary mechanisms of deformation under fatigue stress are analysed in a stainless steel bicrystal by transmission electron microscopy. Attention is paid to the interaction between lattice dislocations and a ferrite-austenite Interface oriented very near the Kurdjumov-Sachs orientation relationship. Results differ according to whether the notch is located in the α phase or in the γ phase. Only in the bicrystal notched in the α phase was transmission of dislocations across the Interface into the γ-phase observed. A possible correlation between the microscopic observations and the fatigue behaviour of the bicrystal is discussed.
-
Interface Structure in Ferritic/Austenitic Stainless Steel Bicrystals
MRS Proceedings, 2000Co-Authors: A. Taisne, B. Decamps, Louisette PriesterAbstract:ABSTRACTElementary mechanisms of deformation by fatigue in duplex stainless steels bicrystals are studied by transmission electron microscopy (TEM). An attempt is made to correlate the bicrystal macroscopic behaviour with the Interphase Interface crystallography.
Gregory A Schoeppner - One of the best experts on this subject based on the ideXlab platform.
-
Evolution of stress and deformations in high-temperature polymer matrix composites during thermo-oxidative aging
Mechanics of Time-Dependent Materials, 2008Co-Authors: K. V. Pochiraju, G P Tandon, Gregory A SchoeppnerAbstract:This paper presents a model-based analysis of thermo-oxidative behavior in high-temperature polymer matrix composite (HTPMC) materials. The thermo-oxidative behavior of the composite differs from that of the constituents as the composite microstructure, the fiber/matrix Interphase/Interface behavior and damage mechanisms introduce anisotropy in the diffusion and oxidation behavior. Three-dimensional Galerkin finite element methods (GFEM) that model the thermo-oxidative layer growth with time are used together with homogenization techniques to analyze lamina-scale behavior using representative volume elements (RVEs). Thermo-oxidation-induced shrinkage is characterized from dimensional changes observed during aging in inert (argon) and oxidative (air) environments. Temperature-dependent macro-scale (bulk) mechanical testing and nano-indentation techniques are used for characterizing the effect of oxidative aging on modulus evolution. The stress and deformation fields in a single ply unidirectional lamina are studied using coupled oxidation evolution and non-linear elastic deformation analyses. Deformation and stress states are shown as a function of the aging time. While the thermo-oxidative processes are controlled by diffusion phenomenon in neat resin, the onset and propagation of damage determines the oxidative response of an HTPMC.
-
evolution of stress and deformations in high temperature polymer matrix composites during thermo oxidative aging
Mechanics of Time-dependent Materials, 2008Co-Authors: K. V. Pochiraju, G P Tandon, Gregory A SchoeppnerAbstract:This paper presents a model-based analysis of thermo-oxidative behavior in high-temperature polymer matrix composite (HTPMC) materials. The thermo-oxidative behavior of the composite differs from that of the constituents as the composite microstructure, the fiber/matrix Interphase/Interface behavior and damage mechanisms introduce anisotropy in the diffusion and oxidation behavior. Three-dimensional Galerkin finite element methods (GFEM) that model the thermo-oxidative layer growth with time are used together with homogenization techniques to analyze lamina-scale behavior using representative volume elements (RVEs). Thermo-oxidation-induced shrinkage is characterized from dimensional changes observed during aging in inert (argon) and oxidative (air) environments. Temperature-dependent macro-scale (bulk) mechanical testing and nano-indentation techniques are used for characterizing the effect of oxidative aging on modulus evolution. The stress and deformation fields in a single ply unidirectional lamina are studied using coupled oxidation evolution and non-linear elastic deformation analyses. Deformation and stress states are shown as a function of the aging time. While the thermo-oxidative processes are controlled by diffusion phenomenon in neat resin, the onset and propagation of damage determines the oxidative response of an HTPMC.
A. Taisne - One of the best experts on this subject based on the ideXlab platform.
-
Interaction of lattice dislocations with the α-γ Interphase Interface in a stainless steel bicrystal
Philosophical Magazine A, 2002Co-Authors: A. Taisne, B. Decamps, Louisette PriesterAbstract:Abstract The elementary mechanisms of deformation under fatigue stress are analysed in a stainless steel bicrystal by transmission electron microscopy. Attention is paid to the interaction between lattice dislocations and a ferrite-austenite Interface oriented very near the Kurdjumov-Sachs orientation relationship. Results differ according to whether the notch is located in the α phase or in the γ phase. Only in the bicrystal notched in the α phase was transmission of dislocations across the Interface into the γ-phase observed. A possible correlation between the microscopic observations and the fatigue behaviour of the bicrystal is discussed.
-
Interface Structure in Ferritic/Austenitic Stainless Steel Bicrystals
MRS Proceedings, 2000Co-Authors: A. Taisne, B. Decamps, Louisette PriesterAbstract:ABSTRACTElementary mechanisms of deformation by fatigue in duplex stainless steels bicrystals are studied by transmission electron microscopy (TEM). An attempt is made to correlate the bicrystal macroscopic behaviour with the Interphase Interface crystallography.
A. Schaff - One of the best experts on this subject based on the ideXlab platform.
-
Numerical analysis of composite systems by using Interphase/Interface models
Computational Mechanics, 1997Co-Authors: J. L. Chaboche, R. Girard, A. SchaffAbstract:The paper considers two classes of approaches for the numerical analysis of composite systems: the first one discretizes the assumed Interphase (between matrix and fibre) as volumic elements and uses material models that degenerate from Continuum Damage Mechanics. The second one introduces Interface elements that relate non linearly the normal and tangential tractions to the corresponding displacement discontinuities, incorporating a progressive decohesion, following the lines of Needleman (1987) and Tvergaard (1990). The respective capabilities of these two approaches are discussed on the basis of some numerical results obtained for a unidirectional metal matrix composite system. When the models are consistently adjusted they are able to reproduce the same kind of results. The advantages of the second class of method is underlined and two new versions of Interface models are proposed that guarantee the continuity and the monotonicity of the shear stiffness between the progressive decohesion phase and the subsequent contact/friction law that plays role under compressive shear after complete separation.
-
numerical analysis of composite systems by using Interphase Interface models
Computational Mechanics, 1997Co-Authors: J. L. Chaboche, R. Girard, A. SchaffAbstract:The paper considers two classes of approaches for the numerical analysis of composite systems: the first one discretizes the assumed Interphase (between matrix and fibre) as volumic elements and uses material models that degenerate from Continuum Damage Mechanics. The second one introduces Interface elements that relate non linearly the normal and tangential tractions to the corresponding displacement discontinuities, incorporating a progressive decohesion, following the lines of Needleman (1987) and Tvergaard (1990). The respective capabilities of these two approaches are discussed on the basis of some numerical results obtained for a unidirectional metal matrix composite system. When the models are consistently adjusted they are able to reproduce the same kind of results. The advantages of the second class of method is underlined and two new versions of Interface models are proposed that guarantee the continuity and the monotonicity of the shear stiffness between the progressive decohesion phase and the subsequent contact/friction law that plays role under compressive shear after complete separation.
