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Full-Text Articles in Mechanical Engineering

Ultrasonic Propagation Through A Surface With A Step Discontinuity: Validation Of A Hybrid, Gauss-Hermite Ray Tracing Beam Model, M. Greenwood, J.-L. Mai, A. Minachi, I. Yalda-Mooshabad, R. Bruce Thompson Jan 1993

Ultrasonic Propagation Through A Surface With A Step Discontinuity: Validation Of A Hybrid, Gauss-Hermite Ray Tracing Beam Model, M. Greenwood, J.-L. Mai, A. Minachi, I. Yalda-Mooshabad, R. Bruce Thompson

Review of Progress in Quantitative Nondestructive Evaluation

This research continues our cooperative effort to study the effects of large-scale surface roughness on ultrasonic transmission through interfaces and updates our previously-reported results [1], The Center for Nondestructive Evaluation has developed a model for the propagation of ultrasound through a surface and into an isotropic metal and this model is undergoing experimental validation at Battelle PNL. Once validated, this model will be used as an engineering tool to study the effects of surface conditions upon an ultrasonic inspection of nuclear reactor components. The goal is to quantify and develop requirements to limit the adverse effects of surface conditions during ...


Ultrasonic Scattering From Spherically Orthotropic Shells, John Mittleman, Ron Roberts, R. Bruce Thompson Jan 1993

Ultrasonic Scattering From Spherically Orthotropic Shells, John Mittleman, Ron Roberts, R. Bruce Thompson

Review of Progress in Quantitative Nondestructive Evaluation

Concerns over the detectability of embrittlement in high strength alloys has led to studying a simple anisotropic shell model [1] for grain boundaries decorated by precipitates, or otherwise enriched by segregated inhomogenieties. In this model the shell is presumed to be “spherically orthotropic,” having five independent elastic constants and symmetry about the origin of a spherical coordinate system. This structure is analogous to transversely isotropic materials in a Cartesian coordinate system. By studying ultrasonic scattering from such shells (embedded in an isotropic host, and surrounding an isotropic core), we hope to learn whether their presence could be detected, and differentiated ...


Interaction Of Ultrasound With Imperfectly Contacting Interfaces, R. Bruce Thompson Jan 1993

Interaction Of Ultrasound With Imperfectly Contacting Interfaces, R. Bruce Thompson

Review of Progress in Quantitative Nondestructive Evaluation

The need to characterize imperfectly contacting interfaces is encountered in a wide variety of scientific and engineering problems, as illustrated in Fig. 1. Parts (a)–(c) illustrate the stages of diffusion bonding, [1,2] in which the condition of the interface evolves from one of isolated contacts at the initial stages of bonding through one containing distributed micropores, which exist during intermediate stages, to a state in which the material is fully bonded but in which there may be some near-interface microstructural variations. The ability to determine the degree to which bonding has passed through these conditions is presently needed ...


High-Frequency Elastodynamic Boundary Integral Equation Inversion Using Asymptotic Phase Information, R. Roberts Jan 1993

High-Frequency Elastodynamic Boundary Integral Equation Inversion Using Asymptotic Phase Information, R. Roberts

Review of Progress in Quantitative Nondestructive Evaluation

Ultrasonic transmission and scattering in the high frequency regime are important problems in ultrasonic NDE, relating to both scattering from large flaws, and the transmission behavior of an ultrasonic beam in a complex geometry component. Ultrasonic modeling efforts are often confronted with problems for which asymptotic methods such as geometrical diffraction theory (GTD) prove inadequate due to insufficiently high frequency or lack of an appropriate canonical solution, but which are too high in frequency (too large in ka) for conventional numerical methods such as boundary element methods (BEM). The inefficiency of BEM at high frequency arises from the need to ...


Investigation Of Corrosion In Aluminum/Adhesive Lap-Splices Using Pulse-Echo Ultrasonic Techniques, T. C. Patton, D. K. Hsu Jan 1993

Investigation Of Corrosion In Aluminum/Adhesive Lap-Splices Using Pulse-Echo Ultrasonic Techniques, T. C. Patton, D. K. Hsu

Review of Progress in Quantitative Nondestructive Evaluation

Corrosion can exist in any layer of a simple aluminum/adhesive lap-splice. For lap- splices where only one aluminum surface is accessible, first layer corrosion is corrosion that occurs on or under the accessible skin; and second layer corrosion is that which exists behind the adhesive/scrim layer on the upper or lower surface of the inaccessible skin. Many different nondestructive evaluation (NDE) techniques can detect first layer corrosion, and much progress has been made quantifying corrosion that exists in this layer[l]. Due to the layered nature of a lap-splice, second layer corrosion is much more difficult to detect ...


Effects Of Acoustic Scattering At Rough Surfaces On The Sensitivity Of Ultrasonic Inspection, Peter B. Nagy, Laszlo Adler, James H. Rose Jan 1993

Effects Of Acoustic Scattering At Rough Surfaces On The Sensitivity Of Ultrasonic Inspection, Peter B. Nagy, Laszlo Adler, James H. Rose

Review of Progress in Quantitative Nondestructive Evaluation

Ultrasonic inspection of ordinary samples with more or less rough surfaces is an everyday problem in industrial NDE. Contact techniques require flat or other regular (e. g., cylindrical) surfaces of negligible roughness with respect to the acoustic wavelength. Immersion techniques are less susceptible to surface topography, but they still require that the surface radius be larger than the beam diameter and the surface roughness be comparable or less than the wavelength in the immersion fluid. This difference is due to the fact that in immersion inspection surface irregularities do not significantly reduce the energy transmission into the specimen but rather ...


Monte-Carlo Simulation Of Ultrasonic Grain Noise, I. Yalda-Mooshabad, Frank J. Margetan, R. Bruce Thompson Jan 1993

Monte-Carlo Simulation Of Ultrasonic Grain Noise, I. Yalda-Mooshabad, Frank J. Margetan, R. Bruce Thompson

Review of Progress in Quantitative Nondestructive Evaluation

In ultrasonic inspections for small or subtle defects in metals, defect signals may be obscured by grain noise echoes which arise from the scattering of sound by the microstructure of the metal. Models for predicting microstructural noise levels are consequently essential for accurately assessing the reliability of the ultrasonic inspections. Existing noise models, like the independent scatterer model (ISM) [1], are capable of predicting only average noise characteristics, such as the root-mean-square (rms) noise level. Average noise levels, although useful, are not sufficient for assessing detection reliability. One needs to know the manner in which noise signals are distributed about ...


Modeling Ultrasonic Microstructural Noise In Titanium Alloys, Frank J. Margetan, R. Bruce Thompson, I. Yalda-Mooshabad Jan 1993

Modeling Ultrasonic Microstructural Noise In Titanium Alloys, Frank J. Margetan, R. Bruce Thompson, I. Yalda-Mooshabad

Review of Progress in Quantitative Nondestructive Evaluation

Ultrasonic echoes from small or subtle defects in metals may be masked by competing “noise” echoes which arise from the scattering of sound by grains or other microstructural elements. Algorithms for estimating the detectability of such defects consequently require quantitative models for microstructural noise. In previous work [1,2] we introduced an approximate noise model for normal-incidence immersion inspections using tone-burst pulses, and we used the model to estimate signal/noise ratios for brittle (hard-alpha) inclusions in titanium alloys. In the present work we consider an extension of that noise model to inspections using broadband incident pulses. Like its predecessor ...


Relationships Between Ultrasonic Noise And Macrostructure Of Titanium Alloys, K. Y. Han, R. Bruce Thompson, Frank J. Margetan, James H. Rose Jan 1993

Relationships Between Ultrasonic Noise And Macrostructure Of Titanium Alloys, K. Y. Han, R. Bruce Thompson, Frank J. Margetan, James H. Rose

Review of Progress in Quantitative Nondestructive Evaluation

The complex microstructure of two-phase titanium alloys can produce considerable ultrasonic backscattering noise. The noise introduces problems in detecting small flaws, such as hard-alpha inclusions, by forming a background which can mask the flaw signals. Therefore better understanding of grain noise is required to quantify and increase the detectability of the small flaws. As an aid to understanding the grain noise, an independent scattering model was constructed and studied during last two years by Margetan and Thompson. In that model for the backscattered noise generated by a tone burst, the grain noise is described by following equation (1) N(t ...


On The Differentiation Of Diffusion Bond Strength Using The Total Acoustic Energy Reflected From The Bond, G. C. Ojard, Otto Buck, D. K. Rehbein, M. S. Hughes Jan 1993

On The Differentiation Of Diffusion Bond Strength Using The Total Acoustic Energy Reflected From The Bond, G. C. Ojard, Otto Buck, D. K. Rehbein, M. S. Hughes

Review of Progress in Quantitative Nondestructive Evaluation

Diffusion bonding is a well known metallurgical joining technique which allows similar and dissimilar materials to be bonded together in near net shape. Due to this feature, wider use of this technique is now being made, especially in aerospace industries. Therefore, the differentiation of diffusion bonds with little variation in their acoustic response is of critical importance since relatively significant changes in bond strength may be a consequence. The challenge at the present time is to find ultrasonic techniques that are sensitive enough to detect small changes at the original interface. A number of diffusion bonds has been made that ...


Ultrasonic Scans Using Low Frequency Unresolved Echoes, D. K. Hsu, M. S. Hughes, T. C. Patton Jan 1993

Ultrasonic Scans Using Low Frequency Unresolved Echoes, D. K. Hsu, M. S. Hughes, T. C. Patton

Review of Progress in Quantitative Nondestructive Evaluation

When ultrasonic pulses are used to detect flaws that are near the surface or in thin-layered structures, the natural tendency is to use a narrow pulse. A broadband pulse with a high center frequency and a large bandwidth will allow the flaw echo and interface echoes to be resolved from the front surface echo in an immersion or squirter testing situation. However, there are a number of limitations in using high frequency ultrasound. The major disadvantages are the high attenuation, hence the limited interrogation depth, and the degradation of ultrasonic scan images due to interference effects. Interference fringes can arise ...


The Spatial Resolution Of Rayleigh Wave, Acoustoelastic Measurement Fo Stress, J. C. Johnson, R. Bruce Thompson Jan 1993

The Spatial Resolution Of Rayleigh Wave, Acoustoelastic Measurement Fo Stress, J. C. Johnson, R. Bruce Thompson

Review of Progress in Quantitative Nondestructive Evaluation

One of the challenges in the acoustoelastic measurement of stress is the achievement of high spatial resolution. Since stress induced velocity shifts are generally small (~0.01%), the required precision of time and distance measurements can be quite high for the short propagation distances required. This paper presents a set of design criteria which can guide the experimentalist in choosing the most suitable measurement configuration for Rayleigh wave techniques. Three approaches for measuring the acoustic velocity are considered: measurement of arrival time versus transducer separation for several discrete positions, measurement of arrival time for a pair of transducers at a ...


Crack Length Determination By Ultrasonic Methods, David Kent Rehbein, R. Bruce Thompson, Otto Buck Jan 1993

Crack Length Determination By Ultrasonic Methods, David Kent Rehbein, R. Bruce Thompson, Otto Buck

Review of Progress in Quantitative Nondestructive Evaluation

Accurate calculation of the stress intensity factor on a given component under load relies on an accurate size determination of the flaws present in the component. The challenge to the NDE community has been development of reliable techniques to provide that accurate size determination. Many research groups have investigated this problem using ultrasonic methods with summaries of their techniques and results provided by various authors [1–3]. In general, the techniques developed fall into three general categories; (1) determination of crack length from signal amplitude measurements, (2) determination of crack length from time-of-flight measurements, and (3) determination of crack length ...


Ultrasonic Inspection, Material Noise And Surface Roughness, Mehmet Bilgen, James H. Rose, Peter B. Nagy Jan 1993

Ultrasonic Inspection, Material Noise And Surface Roughness, Mehmet Bilgen, James H. Rose, Peter B. Nagy

Review of Progress in Quantitative Nondestructive Evaluation

The ultrasonic detection of subsurface flaws, such as cracks or voids, may be greatly degraded by the presence of rough surfaces [1,2]. The loss of signal-to-noise arises for three reasons. First, the randomization of the phase of the wave by the roughness may reduce the phase coherent signal from the flaw. Second, additional noise is generated directly by the reflection of the incident beam by the rough surface. Finally, the material noise is modified.


Theory Of Ultrasonic Backscatter From Multiphase Polycrystalline Solids, James H. Rose Jan 1993

Theory Of Ultrasonic Backscatter From Multiphase Polycrystalline Solids, James H. Rose

Review of Progress in Quantitative Nondestructive Evaluation

Ultrasound scatters from the microscopic single crystals that constitute polycrystalline solids. The scattering originates from crystallite-crystallite variations in the density and elastic constants. For single-phase materials, each crystallite has the same density and the same crystalline symmetry. Hence, in single-phase materials scattering arises from the variation in velocity, which in turn is due to the anisotropy of the elastic constants and the more or less random orientation of the crystallites [1,2]. The situation is considerably more complicated in multiphase alloys where the density, the crystal symmetry and the elastic constants vary from crystallite to crystallite.