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Molecular orbital study of hydrated clusters of LiOH

Miyazaki S., Osamura Y.

Bulletin of the Polish Academy of Sciences. Chemistry

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2002

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Vol. 50, No. 4

463-489

EN

The molecular structures of the hydrated species of LiOH, LiOH(H2O)n for n = 1 ~ 5, were studied in terms of density functional B3LYP molecular orbital method. Since the water molecules act as both acid and base toward LiOH, all stable structures located at energy minima are found to be cyclic geometries. The distance between Li+ and OH(-) increases as the number of water molecules increase. Due to the covalent nature of LiOH, the dissociation of LiOH toward Li and OH(-) requires sufficient number of water molecules. Only non-dissociated structures were obtained in the case of a small number of water molecules (n < 3). Even in the case of LiOH(H(2)O)(5), the non-dissociated structures are calculated to be more stable than the dissociated structures. The number of isomers increases substantially with the increase of the number of water molecules. The ionic structures can be classified into contact ion-pair and solvent separated ion-pair structures. The four water molecules can coordinate to Li+ ion and the OH(-) ion can accept three water molecules in most cases. The stabilization energies of hydration for LiOH are calculated to be much larger than those of strong acids such as HCl and H(2)SO(4). The predicted vibrational spectra of each size of clusters indicate an irregular tendency of the stretching frequency of Li-O depending on the number of water molecules.

2

Shape memory alloy preparation for multiaxial tests and identification of fundamental alloy performance

Tanaka K., Kitamura K., Miyazaki S.

Archives of Mechanics

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1999

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Vol. 51, nr 6

785-803

EN

TiNi shape memory alloy preparation for the multiaxial tests was explained. Stable response of the alloy was realized, not by training but by an effective combination of the alloying technique and the heat treatment: Ti-51.0 at%Ni polycrystalline shape memory alloy heat-treated by annealing at 673 K for 3.6 ks followed by cooling in a furnace. Some preliminary tests were performed to identify the fundamental alloy characteristics: the transformation temperatures, the stress-strain curves at several temperatures and the strain-temperature curves under constant hold stresses.

3

Experimental methodology for TiNi shape memory alloy testing under complex stress state

Raniecki B., Dietrich L., Kowalewski Z., Socha G., Miyazaki S., Tanaka K., Ziółkowski A.

Archives of Mechanics

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1999

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Vol. 51, nr 6

727-744

EN

The experimental method and preliminary results of multiaxial proportional loadings at a range of different temperatures are discussed for the TiNi shape memory alloy. The results are limited to the R-phase reorientation and transformation pseudoelasticity of the material tested at the selected constant temperatures. The main objective of the paper is to develop experimental knowledge of the shape memory alloy properties under complex stress states which would allow better understanding of the material behaviour and create a basis for theoretical modelling.

4

Deformation behaviour of TiNi shape memory alloy undergoing R-phase reorientation in torsion-tension (compression) tests

Raniecki B., Miyazaki S., Tanaka K., Dietrich L., Lexcellent C.

Archives of Mechanics

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1999

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Vol. 51, nr 6

745-784

EN

The deformation behaviour associated with the R-phase reorientation is investigated in a Ti-51.0 at%Ni polycrystalline shape memory alloy under the torsion-tension (compression) stress state, and special theoretical framework is developed to describe the observed alloy performance. The limit condition to start the reorientation process, represented as a surface on the axial stress-shear stress plane, is determined for the proportional loading path. The result is well described, not by the Huber-Mises condition (the J2-theory) but by the model (the J3-theory), by taking into account the third invariant of stress deviator through the concept of the shape function. The values of the shape function are determined experimentally. The basic experimental features of the deformation in the R-phase, such as the flow rule, the ratios of the reorientation strain rates and the dimensionless ratio of the reorientation work, are compared with the predictions of theories that neglect the effects of pressure, compressibility of reorientation strains and effects of induced anisotropy. The J3-theory turns out to be more realistic than the J2-theory.