Application-Directed Modeling of Radiation and Prpagation of Elastic Waves in Anisotropic Media: GPSS and OPOSSM

In ultrasonic nondestructive testing use is made of the physical properties of elastic waves in solids in order to detect defects and material inhomogeneities. Difficulties in testing anisotropic materials are due to the direction dependence of the ultrasonic velocities and to the inherent effects of beam divergence and beam distortion. Based on a theory of elastic wave propagation in transversely isotropic media [1], the Generalized Point-Source-Synthesis-method (GPSS) has been developed to model the radiation, propagation and scattering of elastic waves as generated by ultrasonic transducers in these media [2]. The method accounts for the three-dimensionality and the vectorial character of anisotropic wave phenomena and is particularly useful in view of application-directed modeling at low computation times. A specifically interesting outcome is OPoSSM (‘Optimization by Point-Source-Synthesis-Modeling’), which allows optimized dimensioning and build-up of complex transducers according to their selected field of application. In this contribution, results are presented for austenitic weld material and fiber composites, covering echo dynamic curves — in comparison with experimental results — for commercial transducers. Furthermore, OPoSSM-results on optimized TR-array-probes are presented as well as snapshots of transducer-generated wavefronts, impressively illustrating the modeling of time-dependent rf-signals

Elastic Wave Propagation and Scattering in Austenitic Steel

Ultrasonic nondestructive testing of austenitic steel welds is very difficult, because fundamental wave propagation and scattering effects in such complicated anisotropic environments are only hardly understood [1, 2]. Therefore, a step-by-step evaluation of elastic wave propagation in transversely isotropic media has been initiated. Under the assumption of transverse isotropy the numerical EFIT code (Elastodynamic Finite Integration Technique) [3] - [7] was extended to anisotropic homogeneous media. It allows 3D computation of quasi pressure and quasi shear as well as surface waves in transverse isotropic media. Results for finite aperture transducer radiation and crack scattering in a single crystal austenitic weld are presented; measurements of amplitude dynamics, A-Scans and C-Scans confirm the EFIT simulations [8]

Catching VY Sculptoris in a low state

Context. In the context of a large campaign to determine the system parameters of high mass transfer cataclysmic variables, we found VY Scl in a low state in 2008. Aims. Making use of this low state, we study the stellar components of the binary with little influence of the normally dominating accretion disc. Methods. Time-resolved spectroscopy and photometry of VY Scl taken during the low state are presented. We analysed the light-curve and radial velocity curve and use time-resolved spectroscopy to calculate Doppler maps of the dominant emission lines. Results. The spectra show narrow emission lines of Halpha, Hbeta, HeI, NaID, and FeII, as well as faint TiO absorption bands that trace the motion of the irradiated secondary star, and Halpha and HeI emission line wings that trace the motion of the white dwarf. From these radial velocities, we find an orbital period of 3.84 h, and put constraints on binary parameters such as the mass ratio M2/M1 of 0.43 and the inclination of 15 deg. With a secondary's mass between 0.3 and 0.35 Msol, we derive the mass for the white dwarf as M1 = 0.6-0.1 Msol.Comment: 8 pages, 9 figures, accepted for publication in A&

Transformation textures in post-perovskite: Understanding mantle flow in the D '' layer of the Earth

Deformation and texture formation in (Mg, Fe)SiO3 post perovskite (ppv) is a potential explanation for the strong seismic anisotropy that is found in the D '' layer of the Earth. However, different experimental approaches have resulted in different lattice preferred orientations (LPO) in deformed ppv that have led to ambiguity in the interpretation of deformation in the lowermost mantle. Here, we show that deformation of the analogue substance CaIrO3 during a phase transformation from perovskite to ppv leads to a transformation texture that differs from the CaIrO3 ppv deformation texture but resembles the results from ppv deformation experiments in diamond anvil cells. Assuming material spreading parallel to the core-mantle boundary, our results predict a widespread shear wave splitting with fast horizontal S-waves, which is compatible with seismic studies. Downwelling material that undergoes a phase transformation may develop a transformation texture that would locally result in vertically polarized fast S-waves. Citation: Walte, N. P., F. Heidelbach, N. Miyajima, D. J. Frost, D. C. Rubie, and D. P. Dobson (2009), Transformation textures in post-perovskite: Understanding mantle flow in the D '' layer of the Earth, Geophys. Res. Lett., 36, L04302, doi: 10.1029/2008GL036840

Experimental Evaluation of Ultrasonic Simulation Techniques in Anisotropic Material

The high performance of the available computer technology provides the possibility to simulate the real life for ultrasonic inspections in terms of primary ultrasonic data like rf-time signals. For isotropic material codes like Generalized Point Source Synthesis (GPSS) or Elastodynamic Finite Integration Technique (EFIT) and the theoretical predictions correlate well with experimental results. Recently, the codes mentioned above have been extended to operate also in anisotropic material. In a first step the codes GPSS and EFIT have been expanded to work in materials of parallel oriented columnar grain structure with transversely isotropic symmetry. In order to verify these codes a set of experiments was carried out on weld metal pads and on welds of defined grain structure. Radiation, propagation, reflexion on boundaries and interaction of the sound field with defects for the modes “through transmission” and “pulse echo” were simulated and compared with the experiment

Crack detection and defect classification using the LLT-technique

A method in current use for defect detection in thick walled components is the tandem technique (1). With the aim to replace this cumbersome two-probe technique, a high sensitivity one-probe technique for the detection of perpendicularly oriented cracks and lack of fusion defects has been developed (2-4). The high sensitivity of this so-called LLT-technique results from the effective mode conversion at the defect from a longitudinal wave and the exploitation of the specular reflections. In comparison to the tandem technique the LLT-technique shows an improved defect localization, improved acessibility of the inspection regions, minor obliquity dependence and minor cladding effects in the inspection of cladded components from the outside. Further, mode conversion effects can be used for a defect classification

Application-Directed Modeling of Radiation and Prpagation of Elastic Waves in Anisotropic Media: GPSS and OPOSSM

In ultrasonic nondestructive testing use is made of the physical properties of elastic waves in solids in order to detect defects and material inhomogeneities. Difficulties in testing anisotropic materials are due to the direction dependence of the ultrasonic velocities and to the inherent effects of beam divergence and beam distortion. Based on a theory of elastic wave propagation in transversely isotropic media [1], the Generalized Point-Source-Synthesis-method (GPSS) has been developed to model the radiation, propagation and scattering of elastic waves as generated by ultrasonic transducers in these media [2]. The method accounts for the three-dimensionality and the vectorial character of anisotropic wave phenomena and is particularly useful in view of application-directed modeling at low computation times. A specifically interesting outcome is OPoSSM (‘Optimization by Point-Source-Synthesis-Modeling’), which allows optimized dimensioning and build-up of complex transducers according to their selected field of application. In this contribution, results are presented for austenitic weld material and fiber composites, covering echo dynamic curves — in comparison with experimental results — for commercial transducers. Furthermore, OPoSSM-results on optimized TR-array-probes are presented as well as snapshots of transducer-generated wavefronts, impressively illustrating the modeling of time-dependent rf-signals.</p