Angular Dependence of Ultrasonic Waves Scattered from Flat Bottom Holes

I would like to present some of our results on angular and frequency dependence of sound scattering from flaws which are two-dimensional and have sharp edges, and specifically on our study of the end of the flat bottom hole, which may be considered as a circular aperture or disk in an infinite medium

Models for the Frequency Dependence of Ultrasonic Scattering from Real Flaws

My objective is to help develop a quantitative working model for a typical nondestructive testing system. Specifically, our objective is to relate the parameters which characterize a defect s~ch as size, orientation, and shape to the ultrasonic scattering field parameters such as amplitude, frequency, scattering angle, and polarization or mode conversion. In Fig. 1 is shown a flat surface sample immersed in liquid containing a real flaw a certain distance below the surface; i.e., in the bulk of the material. Sound waves propagate through the liquid and for the simplest case the wave front enters such that only incident longitudinal waves are present. The waves .at the flaw are scattered, and also mode converted; the scattered wave, which will now be both shear and longitudinal will be reconverted back to a longitudinal wave once leaving the solid body and picked up by a receiver oriented at some angle

Frequency Dependence of Ultrasonic Wave Scattering from Cracks

Studies of spectral analysis of the scattered longitudinal and shear waves from crack-like flaws in solids were carried out in the region of ka ≥ 1. Experimental data are analyzed and compared to two new theories developed recently for elastic wave-diffraction from cracks. These theories relate the amplitude spectra of scattered L and S waves to crack parameters such as size, orientation, surface roughness, etc. On the development of the interpretation obtained from phase spectral information the scattered phase from spherical cavities was calculated from exact theory and compared to experimental data

Diffraction of Ultrasonic Waves by Elliptical Cracks in Metals

Ultrasonic spectrum analysis is used to study the frequency and angular behavior of diffracted longitudinal waves from elliptical cracks with arbitrary orientation in diffusion bonded titanium alloy. The aspect ratio of the cracks (ratio of major to minor axis) ranged from 1 to 8 and the bandwidth of the input signal was such that the scattering diameter was ka ≥ l. The experimental data are analyzed based on a recently developed elastodynamic diffraction theory (by Achenbach et al.). Some of the key parameters of the scattering data are identified to address the inverse problem

Scattering Induced Attenuation of Ultrasonic Backscattering

Scattering induced ultrasonic attenuation offers a simple way to characterize material inhomogeneities. This method has a wide range of applications from tissue characterization [1,2] to ultrasonic NDE, such as grain size measurement in polycrystalline materials [3,4], structural diagnostics in ceramics [5,6], porosity assessment in cast metals [7,8] and composites [9], etc. The scattering induced attenuation of a through transmitted coherent ultrasonic wave can be readily related to certain characteristics of the average inhomogeneity via its total scattering cross-section. In many cases however, ultrasonic attenuation measurement is not feasible except from the backscattered signal. For want of better approximation, the scattering induced attenuation is presumed to have the same relation to the average inhomogeneity as if it were measured by the simpler transmission technique. It was recently reported [10] that this approximation breaks down in porosity assessment, and it probably does not work in many other NDE applications either

Eddy Current Evaluation of Porous Magnesium Alloy Casting

Metal matrix composites (MMCs) have increasingly found a home in high technology industries. Even though much research and money have been invested in their conception, manufacturing and incorporation into load bearing structures, the development of suitable nondestructive evaluation technique to test their integrity has lagged behind. Eddy current testing may provide a suitable method of inspection the internal structure of MMCs through differences in electrical conductivity and/or magnetic permeability between fibers and matrix

Elastic Waves Scattering from Corrugated Metal Interfaces

This is a study of elastic waves diffracted by corrugated metallic surfaces. The corrugations consist of triangular grooves with variable parameters. The results of the narrow band experiments show significant diffraction patterns depending on angle and frequency. In addition, a continuous schlieren system is used to visualize the diffracted orders. Measurements were also carried out using a broadband pulse echo system. The behavior of the received spectra is characteristic of the surface profile. Both front and back surfaces have been investigated

Elastic Wave Scattering from Griffith Cracks

To model elastic wave scattering from fatigue cracks in metals, studies were conducted of wave scattering from artificial cracks using ultrasonic spectroscopy. The cracks are of two dimensional planar strips oriented at various angles and embedded in diffusion bonded titanium alloy. The crack is assumed to behave as a Griffith crack and expressions (derived by Achenbach) to describe diffracted field of elastic waves are used to analyze experimental results