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## Full-Text Articles in Engineering Science and Materials

Test Bed For Quantitative Nde, R C. Addison Jr, R B. Houston, J F. Martin, R Bruce Thompson

#### Test Bed For Quantitative Nde, R C. Addison Jr, R B. Houston, J F. Martin, R Bruce Thompson

*Review of Progress in Quantitative Nondestructive Evaluation*

The ARPA/AFML Interdisciplinary Program for Quantitative Flaw Definition has demonstrated a number of new techniques for quantitatively sizing flaws, as are reported elsewhere in these proceedings. This paper describes the progress that has been made during the past year on a test bed program to assemble and demonstrate these techniques in a single integrated measurement system that will extend them from the idealized geometries that have been considered thus far to geometries that are a better approximation to those that are found in real parts. The basic system consists of a Data General Eclipse S/200 Minicomputer, a multiaxis ...

Application Of Emats To In-Place Inspection Of Railroad Rails, H Maiseri, D Maclauchlan, George A. Alers

#### Application Of Emats To In-Place Inspection Of Railroad Rails, H Maiseri, D Maclauchlan, George A. Alers

*Review of Progress in Quantitative Nondestructive Evaluation*

With the aging of the U.S. railroad system and the increased tonnage being moved, it is more important than ever to monitor the installed railroad track for defects whose growth could lead to track failure and derailments. Current ultrasonic inspection techniques utilize a liquid filled wheel to couple acoustic energy from several piezoelectric transducers into the rail at a variety of angles relative to the head of the rail. This approach limits the speed of inspection to approximately 10 mph, is very sensitive to the surface condition and orientation of the railhead and requires frequent maintenance stops. The feasibility ...

Industrial Problems Encountered In The Eddy Current Inspection Of Steel, G V. Jeskey, F P. Vaccaro

#### Industrial Problems Encountered In The Eddy Current Inspection Of Steel, G V. Jeskey, F P. Vaccaro

*Review of Progress in Quantitative Nondestructive Evaluation*

It is anticipated, that through exposing some of the problems encountered in industrial applications of eddy current technology, technical assistance may be generated through the theoretical community. The specific problem examined involves the development, storage'and utilization of calibration masters. Although the use of probes versus coils greatly reduces the number of calibration masters in that probes are not sensitive to overall geometry and mass variations, the eddy current response is influenced by near probe geometry variations. At present, an empirically derived algorithm is relied upon to characterize this phenomenon although it is hoped that an appropriate theoretical model will ...

The Analytic Signal Magnitude For Improved Ultrasonic Signatures, Paul M. Gammell

#### The Analytic Signal Magnitude For Improved Ultrasonic Signatures, Paul M. Gammell

*Review of Progress in Quantitative Nondestructive Evaluation*

Conventional pulse-echo ultrasonic receivers rectify the received signal. Because the signature of the reflecting interfaces is modulated by the predominant ultrasonic frequency, interpretation of this signal in terms of the structure of the reflecting interfaces is difficult. Smoothing, as by an R-C filter, ameliorates this effect, giving a less confusing display at the expense of resolution. The magnitude of the analytic signal, on the other hand, represents the shape of the energy packets arriving from the reflecting interfaces. Since this signature is free of modulation effects, interpretation of the signal in terms of the reflecting interfaces is more straightforward. Furthermore ...

The Impedance Of A Loop Near A Conducting Half-Space, Afroz J. M Zaman

#### The Impedance Of A Loop Near A Conducting Half-Space, Afroz J. M Zaman

*Review of Progress in Quantitative Nondestructive Evaluation*

The change in complex impedance between an ideal one-turn circular coil located above and parallel to a conducting half-space with respect to a similar isolated coil has been calculated. From this result a series expansion of the integrand allows the solution to be approximated by terms expressed as complete elliptic integrals. Results have been calculated for the change in impedance as a function of the lift-off distance and the conductivity of the half-space for a coil of representative.radius.

Progress In Solving The 3-Dimensional Inversion Problem For Eddy Current Nde, T G. Kincaid, K Fong, M V. K Chari

#### Progress In Solving The 3-Dimensional Inversion Problem For Eddy Current Nde, T G. Kincaid, K Fong, M V. K Chari

*Review of Progress in Quantitative Nondestructive Evaluation*

The eddy current NDE inversion problem is to determine the parameters of a flaw from the measured eddy current sensor impedance changes. Mathematically, this requires finding the transformation which gives the sensor impedance changes in terms of the flaw parameters, and then inverting this transformation. Finding the transformation is called the forward problem, and finding the inverse of the transformation is equivalent to the inversion problem. The principal difficulty in solving the forward problem is finding solutions to Maxwell's equations in the complex geometries involved. This paper describes a solution to the forward problem which is valid for ellipsoidal ...

Microwave Eddy-Current Techniques For Quantitative Nde, A J. Bahr

#### Microwave Eddy-Current Techniques For Quantitative Nde, A J. Bahr

*Review of Progress in Quantitative Nondestructive Evaluation*

The objective of this research program is to develop microwave scattering techniques for obtaining quantitative information about the characteristic dimensions of surface cracks in metals. Work carried out during the past year has emphasized experimental techniques. The use of an IF bridge and a nearfield dielectric probe to improve the sensitivity of our 100-GHz eddy-current measurement system is described. The results of measurements made on fatigue cracks in 2024-T3 aluminum using this improved system also are presented. The interpretation of these data to provide information about crack depth is explained in terms of a simple model. Finally, a theoretical approach ...

Surface Flaw Detection With Ferromagnetic Resonance Probes, B A. Auld, F Muennemann, D K. Winslow

#### Surface Flaw Detection With Ferromagnetic Resonance Probes, B A. Auld, F Muennemann, D K. Winslow

*Review of Progress in Quantitative Nondestructive Evaluation*

Eddy current methods of flaw detection have been in use for many years. Frequencies used in this type of flaw detector normally range from tens of kilohertz to a few megahertz. We report on recent progress using a resonant probe which operates in the gigahertz frequency range, and compare its performance with classical eddy current methods.

Crack Depth Measurements With The Aid Of Saw Nde, Bernard R. Tittmann, L A. Ahlberg, Otto Buck

#### Crack Depth Measurements With The Aid Of Saw Nde, Bernard R. Tittmann, L A. Ahlberg, Otto Buck

*Review of Progress in Quantitative Nondestructive Evaluation*

This report presents results of measurements of crack depth with the aid of acoustic bulk and surface waves. Both simulated and real fatigue cracks were examined. Two techniques were employed, one took advantage of the very efficient mode conversion between acoustic surface waves and shear waves at the crack tip; the other technique used the diffraction of shear waves at the crack tip. Both techniques were used on a number of simulated {spark eroded) and real cracks in Al 2024. In one fatigue specimen which contained an elliptical crack 4.5 mm in length and 1.25 mm in depth ...

Ultrasonic Flaw Characterization In The Resonance Region By The Boundary Integral Equation Method, Lester W. Schmerr Jr., C. Sieck

#### Ultrasonic Flaw Characterization In The Resonance Region By The Boundary Integral Equation Method, Lester W. Schmerr Jr., C. Sieck

*Review of Progress in Quantitative Nondestructive Evaluation*

When the wavelength of the ultrasound being used to characterize a flaw is of the same order of magnitude as the flaw size, conventional low and high frequency scattering approximations fail. In this frequency range, called here the resonance region, numerical methods are necessary. Here we show that one such method, the Boundary Integral Equation (BIE) Method, is an effective tool for solving elastic wave scattering problems in the resonance region provided some important modifications are made in the method as used previously by other authors. To illustrate the BIE method, scattering from a cylindrical void in two-dimensions is considered ...

#### An Exact Theory For Coherent Nondestructive Evaluation: The Application Of The Bojarski Exact Inverse Scattering Theory To The Remote Probing Of Inhomogenous Media, W Ross Stone

*Review of Progress in Quantitative Nondestructive Evaluation*

In an inverse scattering problem, the fields in the inhomogeneous wave equation are known, and it is desired to solve for the source term. N. N. Bojarski has recently derived an Exact Inverse Scattering Theory for such "inverse source" problems. The problem of determining the generalized refractive index (i.e., the complex permeability and dielectric constant for an electromagnetic problem, or the velocity and absorption for an acoustic problem) distribution of an inhomogeneous medium from measurements of the fields scattered by the medium can be treated using this theory. This solution is applicable to all remote probing problems, and in ...

Direct Inversion In Complex Geometries, Jack K. Cohen, Norman Bleistein

#### Direct Inversion In Complex Geometries, Jack K. Cohen, Norman Bleistein

*Review of Progress in Quantitative Nondestructive Evaluation*

Progress on the POFFIS high frequency flow imaging method is described. Both theoretical and experimental advances have occurred during the current year. Some success was achieved at imaging an off-axis trailer hitch flaw. However, the issue of variable speed was not completely resolved and research on this issue will continue.

Exact Inverse Scattering Theory, Norbert N. Bojarski

#### Exact Inverse Scattering Theory, Norbert N. Bojarski

*Review of Progress in Quantitative Nondestructive Evaluation*

The concepts of reference wave slowness (reciprocal of velocity) and an associated free reference space Green's function slowness spectrum are introduced. A modified Kirchoff surface integral, containing only the imaginary part of this free reference space Green's function slowness spectrum, is formulated, yielding an integral equation for the unknown fields and sources in the interior of a closed surface on which the (remotely sensed) fields are known. A well-posed, analytic closed form solution of this integral equation is obtained

Ndt Of Composites By Thermography, P V. Mclaughlin Jr, E V. Mcassey Jr, D N. Koert, R C. Deitrich

#### Ndt Of Composites By Thermography, P V. Mclaughlin Jr, E V. Mcassey Jr, D N. Koert, R C. Deitrich

*Review of Progress in Quantitative Nondestructive Evaluation*

This paper describes ongoing research efforts to evaluate thermographic techniques for locating flaws or damage in structural fiber composite laminates. An infra-red camera with video isotherm readout is used to identify perturbations in uniform or linear thermal fields which may be caused by presence of flaws or damage such as matrix cracks, delaminations, blind side impact damage, and partial through holes. This procedure has potential for rapid qualitative screening of large surface areas. Potential defective areas may then be analyzed by a more accurate (but more time consuming) method . Two techniques are discussed; externally applied thermal field (EATF) and stress-generated ...

Study Program For Encapsulation Materials Interface For Low-Cost Solar Array (Lsa), David H. Kaelble, C L. Leung

#### Study Program For Encapsulation Materials Interface For Low-Cost Solar Array (Lsa), David H. Kaelble, C L. Leung

*Review of Progress in Quantitative Nondestructive Evaluation*

The early validation of a 20 year service integrity for the bonded interfaces in low cost solar arrays is an important requirement in the Low Cost Solar Array ( LSA) project. An atmospheric corrosion model has been developed and verified by five months of corrosion rate and climatology data acquired at Mead, Nebraska LSA test site. Atmospheric corrosion monitors (ACMs) installed at the Mead test site showed that protection of the corroding surface by the encapsulant is achieved independent of climatology variations. A newly designed Mead climatology simulator has been developed in laboratory corrosion studies to clarify corrosion mechanisms displayed by ...

Fracture Mechanics Of Two Dimensional Noncircular Flaws, Roger Chang

#### Fracture Mechanics Of Two Dimensional Noncircular Flaws, Roger Chang

*Review of Progress in Quantitative Nondestructive Evaluation*

The growth of two dimensional noncircular flaws was studied by three independent methods: transfer function analysis, equivalent area approximation, and direct fracture mechanics calculation. All three methods yield results varying within a few percent of one another for the simpler elliptical and rectangular geometries. Results of transfer function and equivalent area methods agree also within a few percent of each other for the more irregularly shaped flaws. The importance of these studies to NDE predictive technology is discussed.

Improved Imaging Of Magnetic Flux Leakage Fields, Alfred L. Broz

#### Improved Imaging Of Magnetic Flux Leakage Fields, Alfred L. Broz

*Review of Progress in Quantitative Nondestructive Evaluation*

The present detection methods for imaging flux leakage are colored particle, fluorescent particle, Hall detectors and coils. These techniques are limited due to the need for the detector to be in close proximity to the· material being inspected. Requirements exist in the Army for both remote sensing techniques and techniques which will allow easier analysis of the detected flux leakage.

Nondestructive Evaluation Of Composite Materials With Backscattering Measurements, Y Bar-Cohen, R L. Crane

#### Nondestructive Evaluation Of Composite Materials With Backscattering Measurements, Y Bar-Cohen, R L. Crane

*Review of Progress in Quantitative Nondestructive Evaluation*

Initial experiments have been performed to characterize the scattering of acoustic waves from glass/ epoxy and graphite/epoxy composite panels. Experiments were conducted in the region 0.1 ≤ ka ≤ 1.0 on both types of fiber reinforced composites. The data clearly show that a maximum in the backscattering ultrasonic energy occurs for orientations which place the fiber axis perpendicular to the propagation vector.

Acoustic Nondestructive Evaluation Of Energy Release Rates In Plane Cracked Solids, R King, George Herrmann, Gordon S. Kino

#### Acoustic Nondestructive Evaluation Of Energy Release Rates In Plane Cracked Solids, R King, George Herrmann, Gordon S. Kino

*Review of Progress in Quantitative Nondestructive Evaluation*

Acoustic measurements, using longitudinal waves in plane specimens, based on the theory of acoustoelasticity, permit the determination of the sum of the principal stresses (σ_{1} + σ_{2}). By automatic scanning, we are able to make such measurements throughout a region of interest. In this paper we shall be concerned with the application of this acoustoelastic stress analysis to fracture mechanics. Specifically, the energy release rates for extension and rotation of a crack will be determined experimentally (J integral for extension, L integral for rotation) followed by a numerical adjustment procedure which may be called the rescaling technique. If desired ...

Planning Activity Report For Nde Of Adhesive Bonded Structures, F N. Kelley, W G. Knauss, David H. Kaelble

#### Planning Activity Report For Nde Of Adhesive Bonded Structures, F N. Kelley, W G. Knauss, David H. Kaelble

*Review of Progress in Quantitative Nondestructive Evaluation*

Following a workshop held at the Rockwell International Science Center, Thousand Oaks, California in January, 1979, an ad hoc planning activity was undertaken to set forth a program plan to address the needs in NDE for adhesive bonded structures. The objectives of the planning activity were to develop a program rationale and strategy, determine the existence of reasonable approaches, and to propose a detailed plan of action for review at the annual DARPA/AF meeting in September, 1979. The plan encompasses the basic elements of an accept/reject methodology based on fracture mechanics, expected developments of valid flaw growth models ...

Energy Release Rates For A Plane Crack Subjected To General Loading And Their Relation To Stress-Intensity Factors, A Golebiewska Herrmann, George Herrmann

#### Energy Release Rates For A Plane Crack Subjected To General Loading And Their Relation To Stress-Intensity Factors, A Golebiewska Herrmann, George Herrmann

*Review of Progress in Quantitative Nondestructive Evaluation*

The well-known J integral of elastic fracture mechanics has been related to potential energy-release rate associated with crack extension and has proved to be of great value in fracture testing. In particular, the path-independence of the J integral has been used to an advantage in performing acoustoelastic measurements along a closed contour surrounding a crack tip. In Mode I (opening mode) for example, the J integral depends essentially only on the corresponding stress intensity factor K_{I}which can thus be determined.

Actually, J is the component of a vector in the plane of the crack and there exists a ...

Evaluation Of The Structural Integrity Of Granular Composites By Ultrasonic Techniques, H R. Carleton, W Burke, W J. Chen

#### Evaluation Of The Structural Integrity Of Granular Composites By Ultrasonic Techniques, H R. Carleton, W Burke, W J. Chen

*Review of Progress in Quantitative Nondestructive Evaluation*

The development of the mechanical strength of composite materials which are consolidated by cementaceous bonds has been monitored by observation of the ultrasonic properties over the evolution of bond growth. The granular nature and weak bonding of these materials produce high attenuation of the ultrasonic signal and observation is difficult, particularly in larger structures. In order to obtain ultrasonic parameters with high resolution and to overcome the effects of grain scattering, a system based on a minicomputer and array processor has been implemented which provides time and frequency-domain processing and aperture synthesis. This ultrasonic data provides a reliable measure of ...

X-Ray Diffraction Evaluation Of Adhesive Bonds And Damage In Composites, Charles S. Barrett, Paul Predecki

#### X-Ray Diffraction Evaluation Of Adhesive Bonds And Damage In Composites, Charles S. Barrett, Paul Predecki

*Review of Progress in Quantitative Nondestructive Evaluation*

Stresses can be measured by X-ray diffraction, not only in metals but also in polymeric composites containing some crystalline filler particles. Diffraction is found effective in disclosing the distribution of stresses over the surface of adhesively bonded joints in aluminum strips when loads well below the yield point are applied. When two 6061-T6 aluminum strips 1/16" or 1/32" thick and 3/4" wide are adhesively bonded in a single lap joint and loaded in tension, maps giving the distribution of the X-ray-measured stresses show clear evidence of the way in which stresses are transferred from one adherend to ...

Remaining Fatigue Lifetime Prediction For Retirement-For-Cause In Metals, W L. Morris, M R. James, Otto Buck

#### Remaining Fatigue Lifetime Prediction For Retirement-For-Cause In Metals, W L. Morris, M R. James, Otto Buck

*Review of Progress in Quantitative Nondestructive Evaluation*

A methodology is evaluated to predict the probability of specimen failure with subsequent fatigue, after a short surface crack has been detected in Al 2219-T851 alloy. Cracks are detected and tracked to failure using optical microscopy. Predictions of remaining lifetime distributions are made with a Monte Carlo procedure in conjunction with growth laws which model the effect of grains of differing size, shape and crystallographic orientation in the crack path on propagation rate. Because the surface of the alloy cyclically hardens, the average rate of crack growth is less for cracks formed later during fatigue. The predictive methodology successfully describes ...

Elastic Waves Scattering From Corrugated Metal Interfaces, A Jungman, Gérard Quentin, Laszlo Adler

#### Elastic Waves Scattering From Corrugated Metal Interfaces, A Jungman, Gérard Quentin, Laszlo Adler

*Review of Progress in Quantitative Nondestructive Evaluation*

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.

Ultrasonic Characterization Of Rough Cracks, M De Billy, F Cohen-Tenoudji, Gérard Quentin, Kent Lewis, Laszlo Adler

#### Ultrasonic Characterization Of Rough Cracks, M De Billy, F Cohen-Tenoudji, Gérard Quentin, Kent Lewis, Laszlo Adler

*Review of Progress in Quantitative Nondestructive Evaluation*

It has been reported before that frequency and angular information from ultrasonic scattering can be used to characterize smooth artificial defects in metals. In this study ultrasonic measurements from fractured and smooth penny-shaped cracks of the same size were carried out. Experimental procedures included the use of broad band and narrow band ultrasonic signals. From angular and frequency dependence of ultrasonic scattering measurements the size, shape, orientation and rms roughness of the fractured surface have been estimated. Ultrasonic measurements of these parameters have been compared to the actual parameters of the defect.

About The Efficiency Of Using "Extended" Fourier Transforms For Surface Characterization By The Deconvolution Technique, F Cohen-Tenoudji, Gérard Quentin

#### About The Efficiency Of Using "Extended" Fourier Transforms For Surface Characterization By The Deconvolution Technique, F Cohen-Tenoudji, Gérard Quentin

*Review of Progress in Quantitative Nondestructive Evaluation*

Deconvolution of echoes scattered by a surface tends to give the response function to a Dirac pulse incident on the surface. In some cases, this response function is easily related to the geometry of the scatterer and could be used to characterize it. In practical, the situation of the Dirac pulse with infinite bandwidth is not realized even by a broad band transducer which acts as a band-pass filter. We propose here some simple arguments to extend the Fourier spectrum in order to improve the results of deconvolution. Experiments are performed with targets consisting either of small plane surfaces of ...

Resonances And Crack Roughness Effects In Surface Breaking Cracks, S Ayter, B A. Auld

#### Resonances And Crack Roughness Effects In Surface Breaking Cracks, S Ayter, B A. Auld

*Review of Progress in Quantitative Nondestructive Evaluation*

This study deals with two different aspects of scattering from the cracks. The first one is the measurement of crack resonances by local probes and the second is the effect of the roughness of the crack forces on the scattering data. Unlike the scattering measurement reported elsewhere, these measurements of crack resonances are to be performed by local probes. Two different types of probes are described and their problems are discussed. The effect of crack roughness on the scattering data is investigated via the reciprocity relation. The crack roughness is analyzed using perturbation theory and the equivalent boundary condition concept ...

Scattering By Surface-Breaking And Sub-Surface Cracks, J D. Achenbach, R J. Brind, A Norris

#### Scattering By Surface-Breaking And Sub-Surface Cracks, J D. Achenbach, R J. Brind, A Norris

*Review of Progress in Quantitative Nondestructive Evaluation*

This paper is concerned with exact solutions and approximate solutions in the high-frequency domain for scattering of time-harmonic waves by surface-breaking cracks and cracks which are located near a free surface. Both incident surface waves and incident body waves have been considered. The high-frequency approximate solutions are generally based on elastodynamic ray theory. Some approximate solutions based on the Kirchhoff approximation have been included for comparison.

Application Of Moot To Scattering Of Elastic Waves From Compound Inclusions, William M. Visscher

#### Application Of Moot To Scattering Of Elastic Waves From Compound Inclusions, William M. Visscher

*Review of Progress in Quantitative Nondestructive Evaluation*

We show how MOOT (method of optimal truncation, a convergent T-matrix scheme) can be used to calculate elastic wave scattering from compound inclusions; i.e. inclusions which themselves contain flaws - inclusions, voids, or cracks. The general equations are derived, and they are solved for a particular axially-symmetric case - a cracked spherical jnclusion immersed in fluid. The crack edge is a circle on the equatorial plane; the crack can extend either inward to the center or outward to the surface of the sphere. Numerical results are given for scattering of acoustic waves from cracked spheres of various materials. Cracked spheres can ...