T-Matrix Calculations for Spheroidal and Crack Like Flaws

Numerical calculations are presented for the scattering of elastic (P- and S-) waves from prolate and oblate spheroids and two-dimensional, rough, crack-like flaws for various angles of incidence, observation and frequencies using the T-matrix approach

Elastic Wave Scattering by Rough Flaws and Cracks

The scattering of elastic waves by three dimensional rough flaws and cracks is analyzed using the T-matrix approach. The scattering cross section is obtained for spheroidal cavities with a periodically corrugated surface which may be used as a model for flaws with a rough surface. The dependence of the scattering cross section on the wavelength of the corrugations is studied as a function of the incident wavelength. Cracks are modelled as degenerate oblate spheroids and the scattering cross section is obtained for incident P-waves, Multiple scattering analysis of two cavities is also discussed with some numerical results

Elastic Wave Scattering from Multiple and Odd Shaped Flaws

Using the T-Matrix or Null Field method elastic wave scattering from the following geometries have been studied (a) Rotationally symmetric configurations consisting of two spheroidal cavities separated by a finite distance and with different eccentricities. Exact calculations are compared with single scattering approximations. The frequency spectra are interpreted for various scattering geometries and compared with experiments. The effect of change in distance between the scatterers is also discussed. (b) Scattering from rotationally symmetric cavities with odd shapes like Pinnochio , Rockwell Science Center sample #73 and Micky Mouse , Rockwell Science Center sample #70 was also studied and compared with numerical results using other techniques as well as experiments. Several ways of studying such problems is also discussed. (c) A numerical technique is proposed to study dynamic stress concentrations

Testing the Inverse Born Procedure for Spheroidal Voids

Previously we have shown that the inverse Born approximation allows an accurate determination of the radius of spherical flaws in Ti. Here we report the results of extending that analysis to spheroidal voids. Both oblate and prolate spheroids are considered. Using scattering amplitude generated by the T-matrix method, we find that both the major and minor axes of 2-1 spheroids are accurately determined. Inversion results using experimental data will be presented for the 2-1 oblate spheroid: a comparison of the experimental and theoretical results will be given

Synthesis and temperature dependent fluorescence properties of nanoscale europium doped yttria derived in presence of tween-80 and beta-alanine

A novel procedure for the synthesis of uniform europium doped yttria powder was developed. It was prepared by chemically growth-controlled method in the presence of surface modifier. A mixture of Tween-80 (polyoxyethylene (20) sorbitate) and β-alanine, was used as surface modifier. The obtained powder was pure and highly crystalline. The powder was also examined via Fourier transformation infra red (FTIR) spectroscopy to determine the presence of nitrate ions along with the powder at pre and post calcination. Thermal behavior of the powder was investigated by thermal gravimetric analysis (TGA) and differential thermal analysis (DTA). High Resolution Transmission Microscopy (HRTEM) reveals that the particle size is around 22 nm. Chemical microanalysis of europium doped yttria was made by energy dispersive spectrum analyzer (EDS) attached along with HRTEM and indicated a Y/Eu atomic ratio 2.1. The fluorescence spectra of calcined powder showed that the Eu3+ ions were in low symmetry bonding sites in the yttria structure

Sensitivity of Failure Prediction to Flaw Geometry

The assumption of ellipsoidal flaw geometry has been widely used in calculations of the probability of structural failure conditioned on nondestructive (ND) measurements. Clearly, in most cases the flaw geometry is not ellipsoidal and in the particular case of cracks the actual geometry may deviate significantly from a degenerate ellipsoid (i.e., a planar crack with an elliptical plan-view shape). We have investigated the sensitivity of a late stage of the evolution of fatigue failure to model errors of the latter type (i.e., deviations from elliptical shape for planar cracks) by considering two different overall theoretical processes. In the first, we start with a non-elliptical crack and calculate its geometry after a given large number of cycles of uniaxial stress applied perpendicular to the crack plane. In the second process, we start with the same crack but perform a simulated set of ND measurements coupled with an inversion procedure based on the assumption of elliptical geometry and then calculate the geometry of this initially elliptical crack after subjection to the above stress history. A measure of sensitivity to model error is then provided by a comparison of the two terminal geometries. Results for several choices of non-elliptical crack shapes and sets of ND measurements will be discussed

Tunability of the dielectric response of epitaxially strained SrTiO3 from first principles

The effect of in-plane strain on the nonlinear dielectric properties of SrTiO3 epitaxial thin films is calculated using density-functional theory within the local-density approximation. Motivated by recent experiments, the structure, zone-center phonons, and dielectric properties with and without an external electric field are evaluated for several misfit strains within +-3% of the calculated cubic lattice parameter. In these calculations, the in-plane lattice parameters are fixed, and all remaining structural parameters are permitted to relax. The presence of an external bias is treated approximately by applying a force to each ion proportional to the electric field. After obtaining zero-field ground state structures for various strains, the zone-center phonon frequencies and Born effective charges are computed, yielding the zero-field dielectric response. The dielectric response at finite electric field bias is obtained by computing the field dependence of the structure and polarization using an approximate technique. The results are compared with recent experiments and a previous phenomenological theory. The tunability is found to be strongly dependent on the in-plane lattice parameter, showing markedly different behavior for tensile and compressive strains. Our results are expected to be of use for isolating the role of strain in the tunability of real ultrathin epitaxial films.Comment: 11 pages, with postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/ant_srti/index.htm