The 2004 Ultrasonic Benchmark Problem - SDH Response Under Oblique Incidence: Measurements and Patch Element Model Calculations

Abstract: An explicit point spread function (PSF) evaluator in the frequency domain is described for an ultrasonic transducer operating in the pulse-echo mode. The PSF evaluator employs the patch element model for transducer field determination and scattered field assessment from a small but finite "point" reflector. The PSF for a planar transducer in a medium has been evaluated in the near and the far field. The computed PSFs were used to deconvolve and restore surface images, obtained experimentally, of a single hole and a five-hole cluster in an Al calibration block. A calibration plot is arrived at for estimating, without the need for deconvolution, the actual diameters of circular reflectors from apparent diameters obtained experimentally for a single-medium imaging configuration. The PSF, when the transducer and the point reflector are in two media separated by a planar interface, was evaluated in the near and far field. The computed PSFs were used to deconvolve and restore subsurface images, obtained experimentally, of flat bottom holes (FBHs) in an Al calibration block. We show that the PSF, in the presence of a planar interface, can be obtained from a single-medium PSF model using an effective single-medium path length concept. The PSFs and modulation transfer functions (MTFs) are evaluated for spherical focused and annular transducers and compared with those for the planar transducer. We identify imaging distances to get better-resolved images when using planar, spherical focused, and annular transducers.

Abstract: The 2006 ultrasonic benchmark problem involves pulse‐echo angle beam scanning of a notch located on an inclined planar back surface. The response from a side‐drilled hole is to be used as a reference. The models are to simulate (a) the peak‐to‐peak B‐scan P‐ and SV‐ responses of the slots normalized by the appropriate SDH response and (b) the maximum peak‐to‐peak corner response of the slots (either mode‐converted or not). At CNDE, several simulation tools are being developed to assess/predict UT response for various geometries. The Finite‐Difference‐Time‐Difference (FDTD) scheme is one such simulation tool that has been under development in 1D, 2D and 3D. The FDTD is an explicit time domain tool that can simulate pulse propagation characteristics in acoustic/elastic media. The computational domain is limited by implementing Perfectly Matched Layers (PMLs) at the domain boundaries. We present the results of calculations based on 2D FDTD to determine the response of rectangular shaped surface‐breaking defe...

Abstract: : This monograph systematically presents methods of solution for both steady-state and transient loading on various obstacles, and also numerical results of dynamic stress concentration on obstacles of different geometries. An effort is made to collect information from the open literature as well as from government agencies, industry, and individuals. (Author-PL)

Abstract: A method is presented for calculation of the sound field from a rectangular continuous-wave source surrounded by a plane grid baffle. The approach is illustrated for square sources of 0.5, 1, 2, 5, 10, 20, and 100 lambda on a side. These results are compared to the sound fields produced by similarly sized circular sources. The beam widths and locations of on-axis minima are similar for the two sources, but the transverse pressure distribution is more uniform in the near-field of the square source. The effects of attenuation on the sound field of a square source are examined. >

Abstract: The principles of pencil elastodynamics and, in more detail, some selected applications of pencil techniques to elastodynamics are described. It is shown how a systematic use of a matrix representation for the wave front curvature and for its transformations simplifies the handling of arbitrary pencils and, consequently, the field computations. Pencil matrix representations for the propagation into homogeneous solids made of isotropic or anisotropic media are derived. The use of matrix representations for pencil reflections on, or refractions through, arbitrarily curved interfaces, together with matrix representations for propagation into homogeneous media, allow us to derive an overall matrix formulation for elastodynamic propagation into complex heterogeneous structures. Combined with the classical Rayleigh integral to account for transducer diffraction effects, the proposed theory is applied to the prediction of ultrasonic fields radiated into complex structures by arbitrary transducers. Examples of interest for application to ultrasonic non-destructive testing are given.

Abstract: A new method for simulating the propagation of pulses radiated by a circular normal ultrasonic transducer which is directly coupled to a homogeneous and isotropic elastic half-space is proposed Both nonuniform and uniform high-frequency asymptotics inside geometrical regions as well as boundary layers (penumbra, an axial region, and a vicinity of the critical rays) have been used to describe the transient field by means of harmonic synthesis The nonuniform asymptotic formulas involving elementary or well-known special functions elucidate the physics of the problem and give explicit dependence of the radiated waves upon the model parameters The formulas are applicable in the radiating near field which is the near-field with the evanescent wave zone excluded The code based on the uniform asymptotics has been tested in all regions against an exact numerical solution It is orders of magnitude faster, but in many realistic cases the accuracy does not suffer The limits of applicability of the model have been established