Key Engineering Materials Vols. 353-358

Abstract: This paper presents the simple method to determine the complex stress intensity factor of interface crack problem by the finite element method. The proportional method is extended to the interface crack problem. In the present method, the stress values at the crack tip calculated by FEM are used and the stress intensity factors of interface crack are evaluated from the ratio of stress values between a given and a reference problems. A single interface crack in an infinite bi-material plate subjected to tension and shear is selected as the reference problem in this study. The accuracy of the present analysis is discussed through the results obtained by other methods. As the result, it is confirmed that the present method is useful for analyzing the interface crack problem.

Abstract: In: Eu: Fe: LiNbO3 crystals were firstly grown from a congruent melt according to the Czochralski method, with the various ratios of Li/Nb =0.885, 0.946, 1.051. The new crystal composition and defect structure were analyzed by the UV-Vis spectroscopy. In the two-wave coupling experiments, writing and erasure time, maximum diffraction efficiency, photorefractive sensitivity and dynamic range were measured and calculated. The dependence of the photorefractive properties on the defect structure of In: Eu: Fe: LiNbO3 Crystals were discussed.

Abstract: A series of Al-Si hypoeutectic alloy ingots were prepared by centrifugal casting (CC) both with and without an external electromagnetic field (EMF). The effects the EMF on grain refinement and on the solidification mechanism during centrifugal casting have been investigated using optical microscopy, scanning electron microscopy (SEM) and electron backscattering diffraction (EBSD) orientation measurements. The electromagnetic stirring effect caused by the EMF promotes the columnar-equiaxed transition (CET) resulting in a finer cast grain size. The silicon and aluminum nucleate and grow independently both with and without EMF

Abstract: The microstructure and ferroelectric domains of SrBi2Ta1.6Nb0.4O9 ceramics were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) equipped with energy dispersive spectroscopy (EDS). The X-ray diffraction patterns show that the lattice constants a and b decrease, and c increases by doping with Nb into SBT sample. Accordingly, it has large strain and lattice distortion in the lattice This suggests that the Nb atoms partially occupy the location of the Ta atoms in the lattice. From TEM observations, the grains show (008) preferred orientations in the sample, which agrees well with the XRD results. The 90° domain walls are identified by the 90° rotation relationship of the electron diffraction pattern about the [001] zone axis. The 180° domain walls and anti-phase boundaries (APBs) in Nb-doped SBT ceramics are also observed, which are irregularly shaped and highly curved. The traditional α-fringes can be found in the Nb-doped SBT ceramics, which are the evidence of large strains in the lattice.