1,721,167 research outputs found
Theoretical study for solvent effect on the potential energy surface for the double proton transfer in formic acid dimer and formamidine dimer
No full textDouble proton transfers in formic acid dimer and formamidine dimer were studied as prototypes of multiple proton transfer. The potential energy surface (PFS) for the double proton transfer was studied using ab initio quantum mechanical methods. The solvent effect on the PES was also included using the Onsager self-consistent reaction field model. In the gas phase, the transition state for the double proton transfer in the formic acid dimer complex has D-2h symmetry, but in water it is changed to a C-2v structure, when the Hartree-Fock (HF) level of theory is used. When the density functional theory is used, the transition state has D-2h symmetry with and without solvent. However the barrier height depends very much on the electron correlation. The double proton transfer occurs synchronously in all the cases. For the formamidine dimer complex, the transition state has C-2v symmetry in the gas phase, and it changes to C-s symmetry in water at the HF level of theory. The C-2v structure becomes an intermediate in water, which means that double proton transfer occurs asynchronously. In the density functional theory for the gas phase, the transition state has D-2h symmetry, and it changes to C-2v structure in solution. However the double proton transfer occurs synchronously in both cases. These results suggest that the correlation is very important to the PES for double proton transfer, not only in the gas phase but also in solution
HIGH SPEED TENSILE TEST OF STEEL SHEETS FOR THE STRESS-STRAIN CURVE AT THE INTERMEDIATE STRAIN RATE
No full textThis paper presents stress-strain curves of steel sheets for an auto-body obtained at intermediate strain rates with a servo-hydraulic type high speed tensile testing machine. The apparatus has the maximum stroke velocity of 7.8 m/sec to obtain the tensile material properties at a strain rate of up to 500/sec. A special jig fixture is specially designed for accurate acquisition of tensile loads with reduction of the load-ringing phenomenon induced by unstable stress wave propagation at high strain rates. Tensile testing of steel sheets for an auto-body was carried out to obtain stress-strain curves of mild steel and advanced high strength steels at strain rates ranged from 1/sec to 200/sec. The test results provide interesting information regarding the stress-strain curves at intermediate strain rates ranged from 1/sec to 200/sec and demonstrate that strain rate hardening is strongly coupled with strain hardening
Arbitrariness of asymmetric hat-type channel members in the axial crush
No full textThis paper is concerned with the crashworthiness of asymmetric hat-type specimens that are fabricated by spot welding or laser welding with different spacing between two welded spots. The specimens are evaluated for the axial crush at the various crush velocity. The experimental result shows that the specimens are not deformed in a consistent manner, but arbitrarily. In this type of axial crush, the length of the flange region is an important parameter as well as the spacing between welded spots. Experimental results also show the difference in. the crush mode between the spot-welded specimens and the laser-welded ones. The difference in the first peak and average load is also demonstrated as well as the energy absorption capacity
Combinatorial methods for the selective oxidation of propane to acrylic acid on Mo-V-Te-Nb oxides
No full textVariable-node finite elements with smoothed integration techniques and their applications for multiscale mechanics problems
No full textIn this paper, variable-node finite elements with smoothed integration are proposed with emphasis on their applications for multiscale mechanics problems. The smoothed integration, which picks up strain matrix at discrete points along the cell boundary to form stiffness matrix, is combined with the variable-node finite elements, which have an arbitrary number of nodes on element side Hence, they effectively link meshes of different resolution along their nonmatching interface Particularly, they provide a powerful tool, when combined with homogenization schemes, for multiscale computing for complex heterogeneous structures. We show some applications of variable-node elements for multiscale problems to demonstrate their effectiveness. (C) 2009 Elsevier Ltd All rights reserved.This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean Government (MEST) (No. R0A-2007-000-20115-0)
Development of a Novel Deployment Hinge Mechanism for a Spacecraft Using Axiomatic Design
No full textThermomechanical stress analysis of laminated thick-film multilayer substrates
No full textAs an increasing number of polymer dielectric layers were laminated, the maximum bow values were measured layer by layer using a laser profilometry during thermal cycling. In the lamination process, a polymeric film is overlaid on a silicon substrate using a polymeric adhesive. Since the lamination process uses relatively thick polymer films, the classical stress analyses assuming infinitesimally thin films, are no longer effective. In this letter, a simple model based on the composite beam theory is presented to analyze the experimental results, and compared with the well-known Stoney's formula. The thermomechanical behavior of the laminated multilayer polymer films on a silicon substrate was better described by the proposed model, while an error as much as 30% was involved using Stoney's formula. The model can be applied for the design and fabrication of multilayer multichip module substrates. (C) 1999 American Institute of Physics. [S0003-6951(99)03623-2]
Formability of the steel sheet at the intermediate strain rate
No full textWhile the formability is important and indispensable for success in very complicated sheet metal forming, it seems that few studies has been carried out about the formability of sheet metal at the high strain rate. The present experimental results report that the elongation is dependent on the crosshead speed in tensile tests. In this paper, the tensile elongation has been obtained from various steel sheets for an auto-body at the. intermediate strain rate. The strain rate in the experiment is ranged, from 0.003/sec to 200/sec. The experimental result demonstrates that the tensile elongation does not decrease as the strain rate increases. This tendency has varieties depending on the microstructure and forming history of sheet metal. Some high strength steels have the tendency that the tensile elongation increases as,the strain rate increases, while others not. This phenomenon is very important not only in sheet metal forming but also in the crashworthiness evaluation to predict the fracture and tearing of sheet metal members
A thermomechanical analysis of MCM-D substrate of polymer and metal multilayer
No full textA multichip module (MCM) substrate is an example of multilayer structure under thermal loading. In MCM-D substrate, various thin film technologies are used and the number of layers increases to meet the demands of electronic industry. This multilayer substrate has the properties which are not well taken care of in the usual thermal stress analysis: that is, (i) each layer experiences the different thermal history because the multilayers are made by the sequential buildup of the alternating layers of polymer dielectric and metal conductor films, (ii) a single film thickness cannot be assumed to be infinitesimal any more compared to the others, (iii) the polymer films seem to undergo the relaxation of stress In this study, the thermomechanical bowing was experimentally measured layer-by-layer during the sequential build-up of the alternating layers, and it is compared with the result of the thermomechanical stress analysis of the multilayer MCM-D substrate based on a model which takes into account the different thermal history of each layer and the effect of the film thickness
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