The Experts below are selected from a list of 147 Experts worldwide ranked by ideXlab platform
Lallit Anand - One of the best experts on this subject based on the ideXlab platform.
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grain boundary sliding and separation in polycrystalline Metals Application to nanocrystalline fcc Metals
Journal of The Mechanics and Physics of Solids, 2004Co-Authors: Lallit AnandAbstract:Abstract In order to model the effects of grain boundaries in polycrystalline materials we have coupled a crystal-plasticity model for the grain interiors with a new elastic–plastic grain-boundary interface model which accounts for both reversible elastic, as well irreversible inelastic sliding-separation deformations at the grain boundaries prior to failure. We have used this new computational capability to study the deformation and fracture response of nanocrystalline nickel. The results from the simulations reflect the macroscopic experimentally observed tensile stress–strain curves, and the dominant microstructural fracture mechanisms in this material. The macroscopically observed nonlinearity in the stress–strain response is mainly due to the inelastic response of the grain boundaries. Plastic deformation in the interior of the grains prior to the formation of grain-boundary cracks was rarely observed. The stress concentrations at the tips of the distributed grain-boundary cracks, and at grain-boundary triple junctions, cause a limited amount of plastic deformation in the high-strength grain interiors. The competition of grain-boundary deformation with that in the grain interiors determines the observed macroscopic stress–strain response, and the overall ductility. In nanocrystalline nickel, the high-yield strength of the grain interiors and relatively weaker grain-boundary interfaces account for the low ductility of this material in tension.
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elasto viscoplastic constitutive equations for polycrystalline Metals Application to tantalum
Journal of The Mechanics and Physics of Solids, 1998Co-Authors: M Kothari, Lallit AnandAbstract:Abstract Strain-rate and temperature-dependent constitutive equations for polycrystalline Metals which are capable of modeling the initial and evolving anisotropy in ductile metallic materials owing to the evolution of crystallographic texture are reviewed and then specialized to reproduce the recently published stress-strain response of commercially pure b.c.c. tantalum for strains up to 60%, at strain rates from quasi-static to 30,000 s −1 , and temperatures from −200 to 525 °C (Hoge and Mukherjee, 1977; Vecchio, 1994; Nemat-Nasser and Isaacs, 1996). The constitutive equations have been implemented in a finite element program, and the computational capability is used to simulate the evolution of crystallographic texture in simple compression, plane-strain compression, and torsion under quasi-static conditions. A comparison of the predictions against corresponding experiments shows that the crystal plasticity-based model predicts the texture evolution and the macroscopic stress-strain curves satisfactorily. The computational capability is also used to simulate the dynamic Taylor rod-impact tests performed by Ting (1992) on pre-textured tantalum cylinders. The numerical simulations reasonably reproduce the final length and the ovalized macroscopic shape of the impact end of the cylinders observed in the experiments.
Jean–marie Basset - One of the best experts on this subject based on the ideXlab platform.
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Surface organometallic chemistry on Metals. Application to chemicals and fine chemicals
Topics in Catalysis, 1997Co-Authors: Frédéric Lefebvre, Jean–pierre Candy, Catherine C. Santini, Jean–marie BassetAbstract:Some Applications of surface organometallic chemistry on Metals to catalysis are presented, showing the great importance of the modification of a metallic surface by organometallic compounds on its catalytic properties. The selective hydrogenation of α–β unsaturated aldehydes such as citral (Z and E) can be achieved on rhodium–tin catalysts. While rhodium alone is relatively unselective, geraniol (and nerol) can be obtained selectively (> 98%) without a significant loss of activity by use of a rhodium–tin catalyst showing a typical ligand effect of the organotin fragment on the surface. Similarly, in the isomerization of (+) 3-carene into (+) 2-carene or the dehydrogenation of butan–2–ol into methyl ethyl ketone, the selectivity into the desired product is increased by introduction of small amounts of tin which will form adatoms poisoning unselective sites. An alloying effect of tin is also presented in the dehydrogenation reaction of isobutane in isobutene.
Yufeng Zheng - One of the best experts on this subject based on the ideXlab platform.
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micro alloying with mn in zn mg alloy for future biodegradable Metals Application
Materials & Design, 2016Co-Authors: F Y Zhou, Yinghong Yang, Rencao Chang, Zhongjie Pu, Li Li, Yufeng ZhengAbstract:Abstract Zn as a novel biodegradable metal holds great potential in bioresorbable implant Application since it possesses excellent biocompatibility and more corrosion resistant than Mg. In the present study, the effect of the micro-alloying element Mn on the Zn–Mg alloy was studied with mechanical properties, in vitro degradation behaviors and hemocompatibility being evaluated in comparison with pure Zn as control. The experimental Zn–Mg–Mn alloys were composed of the matrix Zn and secondary phase (MgZn 2 ). Meanwhile, Zn–Mg–Mn alloys ingots exhibited much higher yield strength (YS), ultimate tensile strength (UTS) and hardness compared to pure Zn. But their elongation was reduced. The results of immersion in Hank's solution for 30 days revealed that the sequence of corrosion rates from high to low was: as-cast Zn–1Mg–0.1Mn alloy > as-cast Zn–1.5Mg–0.1Mn alloy > pure Zn. The consequences of electrochemical tests indicated that the calculated corrosion rates followed the ranking order: as-cast Zn–1Mg–0.1Mn alloy > as-cast Zn–1.5Mg–0.1Mn alloy > pure Zn. The results of hemolysis rate and platelet adhesion implied that the studied alloys had good blood compatibility. Furthermore, after hot-rolling, the YS, UTS, elongation and hardness of Zn–1Mg–0.1Mn alloys were further improved and possessed the superior mechanics performance (YS 195.02 MPa, UTS 299.04 MPa, Elongation 26.07%, Hardness 107.82 Hv), appropriate corrosion rate ( V corr 0.25 mm/year) and excellent hemocompatibility (hemolysis rate of 1.10% and no signs of thrombogenicity), showing the preferable candidate as a biodegradable implant material.
Frédéric Lefebvre - One of the best experts on this subject based on the ideXlab platform.
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Surface organometallic chemistry on Metals. Application to chemicals and fine chemicals
Topics in Catalysis, 1997Co-Authors: Frédéric Lefebvre, Jean–pierre Candy, Catherine C. Santini, Jean–marie BassetAbstract:Some Applications of surface organometallic chemistry on Metals to catalysis are presented, showing the great importance of the modification of a metallic surface by organometallic compounds on its catalytic properties. The selective hydrogenation of α–β unsaturated aldehydes such as citral (Z and E) can be achieved on rhodium–tin catalysts. While rhodium alone is relatively unselective, geraniol (and nerol) can be obtained selectively (> 98%) without a significant loss of activity by use of a rhodium–tin catalyst showing a typical ligand effect of the organotin fragment on the surface. Similarly, in the isomerization of (+) 3-carene into (+) 2-carene or the dehydrogenation of butan–2–ol into methyl ethyl ketone, the selectivity into the desired product is increased by introduction of small amounts of tin which will form adatoms poisoning unselective sites. An alloying effect of tin is also presented in the dehydrogenation reaction of isobutane in isobutene.
L P Kubin - One of the best experts on this subject based on the ideXlab platform.
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dislocation study of prismatic slip systems and their interactions in hexagonal close packed Metals Application to zirconium
Acta Materialia, 2004Co-Authors: Ghiath Monnet, Benoit Devincre, L P KubinAbstract:Simulations of dislocation dynamics in single crystals of hcp zirconium are presented with emphasis on the hardening associated with prismatic slip at low temperature. Two original aspects of the simulation method are discussed, the treatment of the hcp lattice by an orthorhombic representation and the use of periodic boundary conditions. The mobility of screw and non-screw segments are defined in a phenomenological manner. Different investigations on the interactions between dislocations gliding in different prismatic planes show that no junction is formed between intersecting screw dislocations, which results in a rather small forest hardening at low temperature. This explains experimental observations of an initial deformation stage with a low strain hardening coefficient in zirconium or titanium crystals at low temperature.