Showing papers in "Journal of Nondestructive Evaluation in 1982"
TL;DR: In this article, the time domain Born approximation for ultrasonic scattering from volume flaws in an elastic medium is described and results for both the direct and the inverse problem are given for both cases.
Abstract: The time domain Born approximation for ultrasonic scattering from volume flaws in an elastic medium is described. Results are given both for the direct and the inverse problem. The time domain picture leads to simple intuitive formulas, which we illustrate by means of several simple examples. Particular emphasis is given to the front surface echo and its use in reconstructing the properties of the flaw.
68 citations
TL;DR: In this article, the interaction between rough crack faces is modeled by nonlinear relations between the crack-face tractions and the crack opening displacements, and the relations are used to investigate reflection and transmission of an incident pulse by an infinite flaw plane.
Abstract: The interaction between rough crack faces is modeled by nonlinear relations between the crack-face tractions and the crack-opening displacements. These relations account for crack closure and for the related resistance to crack-face sliding. The relations are used to investigate reflection and transmission of an incident pulse by an infinite flaw plane. The problem statement is reduced to a set of inhomogeneous nonlinear ordinary differential equations for the displacement discontinuities, [u] and [v], across the flaw plane. These equations have been solved numerically. The reflection and transmission of an incident pulse by a crack with interacting crack faces. Both incident longitudinal and transverse waves have been considered. The loss of specular reflection as compared to a perfect (traction-free) crack is exhibited by specific examples.
41 citations
TL;DR: In this paper, the effect of texture on the acoustoelastic response in polycrystalline bodies was examined and the second and third-order elastic constants of the polycrystal were derived from the elastic properties of the constituent crystals, and the crystalline orientation relative to the body's symmetry axis.
Abstract: Acoustoelasticity is an ultrasonic technique which has been used for the determination of active and residual stresses in common structural materials. This paper examines the effect of texture on the acoustoelastic response in polycrystalline bodies. In particular materials which are transversely isotropic aggregates of cubic crystals are studied. The second- and third-order elastic constants of the polycrystal are derived from the elastic properties of the constituent crystals, and the crystalline orientation relative to the body's symmetry axis. The acoustoelastic relations between velocity and deformation are then presented for the aggregate. Finally, evaluation of the acoustoelastic response for several ideal textures using data for aluminum single crystals shows that the response is highly dependent on the texture.
31 citations
TL;DR: In this paper, an ultrasonic technique to determine the acoustoelastic coefficients of Rayleigh waves in steel alloys is described, based on the measurement of the time of flight of the Rayleigh wave over a fixed surface distance as a function of applied stress.
Abstract: An ultrasonic technique to determine the acoustoelastic coefficients of Rayleigh waves in steel alloys is described. The technique is based on the measurement of the time of flight of Rayleigh waves over a fixed surface distance as a function of applied stress. Measurements on AISI 1080 carbon steel, AISI 4130 alloy steel, and 316L stainless steel specimens are reported. Time of flight resolution and repeatability as well as temperature effects are discussed insofar as they influence the applicability of ultrasonic methods to the measurement of applied and residual biaxial surface stresses in steel.
29 citations
TL;DR: In this paper, a general solution is given to describe the ac field around surface-breaking cracks for arbitrary values of the ratio of skin depth δ to crack depthd, which allows accurate interpretation of crack depth from voltage readings taken by a Crack Microgauge instrument in cases where δ andd are comparable.
Abstract: A general solution is given to describe the ac field around surface-breaking cracks for arbitrary values of the ratio of skin depth δ to crack depthd. This solution allows accurate interpretation of crack depth from voltage readings taken by a Crack Microgauge instrument in cases where δ andd are comparable. It is shown to agree with asymptotic formulae obtained for the cases where δ/d is very small and very large. Provided that the probe length Δ is large compared with δ, the calculations show that a very good approximation to the crack depth may be obtained, irrespective of the ratio δ/d, by using the thin-skin asymptotic formula
$$d = \frac{1}{2}\Delta (V_2 - V_1 )/V_1 $$
whereV1 andV2 are probe voltages registered at positions just off and across the crack, respectively. The problem is solved for a crack of infinite aspect ratio which has no opening, but it can be applied with confidence at the centerline of cracks of fairly large aspect ratio.
24 citations
TL;DR: In this paper, an analytical expression for the change in impedance as a function of the electric fields at the position of the flaw is derived for detecting and characterization of a flaw in a conducting half-space using an eddycurrent coil oriented parallel to the interface.
Abstract: The problem of detection and characterization of a flaw in a conducting half-space using an eddy-current coil oriented parallel to the interface is examined. An expression is derived for a first order approximation for the change in complex impedance due to a flaw located within the conducting medium. The overall impedance is a function of the radius and lift-off distance of the test coil and the conductivity of the material. An analytical expression is derived for the change in impedance as a function of the electric fields at the position of the flaw. It is found to be an integral over the volume of the flaw of the electric fields found with and without the flaw being present. The limiting case of a degenerate point flaw may be examined in greater detail by allowing the field in the presence of the flaw to be approximated by the unperturbed field. For flaws small enough that the field does not vary much over its volume, the field may be even further approximated by using just the value of the field at the position of the centroid of the flaw. Plots are shown to illustrate the behavior of the change in impedance as a function of the radial range of the flaw and the depth of the flaw centroid, using previously derived expressions for the fields for the unflawed case.
23 citations
TL;DR: In this paper, finite element analysis techniques are applied to the problem of predicting signals from an absolute eddy current probe in the tube sheet region of a PWR steam generator for the purpose of optimizing the probe coil geometry.
Abstract: Finite element analysis techniques are applied to the problem of predicting signals from an absolute eddy current probe in the tube sheet region of a PWR steam generator for the purpose of optimizing the probe coil geometry and determining the feasibility of using such a probe to characterize the condition of the tube and tube sheet crevice.
21 citations
TL;DR: In this paper, an approach for treating nondestructive testing as the solution of inverse problems in mathematical physics has been used for the detection of cavities, based on the use of an additional boundary condition of scanned temperature on the surface to solve for the cavity geometry.
Abstract: An approach for treating nondestructive testing as the solution of inverse problems in mathematical physics has been used for the detection of cavities. The approach is developed based on the use of an additional boundary condition of scanned temperature on the surface to solve for the cavity geometry. For the present study, the condition at the cavity side is taken to be that of a specified temperature, and the experiment is carried out to meet this condition. Two specimens are tested in this paper, a plane slab and a rectangular prism. In both bodies the cavity is rectangular in shape. For the testing of the plane slab, the method is able to detect the cavity wall with high accuracy, whereas the cavity depth error is larger (6%). The detection of the cavity position in the rectangular prism has an error ranging from −9.7 to 7.7%. Errors in the experiment are attributed to the uncertainties in the measurements of temperature and the Biot number. The former is read off from the analog data output of the infrared scanner. The latter is not measured separately, but is computed from the scanned data and thus becomes a portion of the total nondestructive testing output. A final note is also made in this paper to relate how the presented method can be used in actual practice.
15 citations
TL;DR: In this paper, the inverse Born approximation was used for the first time in the determination of the size, shape, and orientation of near-surface flaws near a surface of an elastic solid by analyzing the scattered ultrasonic waves.
Abstract: Quantitative reconstruction of volumetric flaws near a surface of an elastic solid has been carried out experimentally by analyzing the scattered ultrasonic waves. The inverse Born approximation (developed for flaws in bulk materials) was tested for the first time in the determination of the size, shape, and orientation of near-surface flaws. We have studied spherical solid inclusions at various depths below the surface. In addition we examined an approximately 2:1 prolate spheroidal inclusion which was located one major axis below the surface. The determination of the flaw's size, shape, and orientation in terms of an equivalent ellipsoid is realized by performing nonlinear least-squares iteration of the one-dimensional Born inversion results obtained at various scattering directions within a finite aperture. The reconstruction is in good agreement with the actual parameters of the flaw.
9 citations
TL;DR: In this article, the authors considered the problem of finding the solution of the skin effect or Helmholtz equation for the two-dimensional flow of a uniform alternating current perturbed by a plane crack of uniform depth.
Abstract: This paper considers the solution of the skin-effect or Helmholtz equation, ∇2ψ=k2ψ, for the two-dimensional flow of a uniform alternating current perturbed by a plane crack of uniform depth. Herek is the ratio of crack depthd to skin depth δ. When the skin depth is large compared with the crack depth andkf 0, the quasi-static approach to this problem ignores the terms on the right-hand side and constructs solutions from Laplace's equation which are essentially dc solutions and are correct to orderk. In this paper we consider behavior near the limit when the skin depth is large and give solutions which are correct to orderk2. In an example we relate the results to the interpretation of readings from an ac potential difference instrument applied to the measurement of surface-breaking cracks.
9 citations
TL;DR: In this article, a pitch-catch Rayleigh wave transducer set-up was used to launch a Rayleigh surface wave at the flaw and to capture and record the scattered waves.
Abstract: An ultrasonic inspection method is used to obtain the circumference of a subsurface hole and the depth of the hole below the surface. A pitch-catch Rayleigh wave transducer set-up was used to launch a Rayleigh surface wave at the flaw and to capture and record the scattered waves. The frequency spectrum of the scattered waves can be used to obtain the depth of the hole. The ligament of material between the hole and the surface is sent into resonance, and this feature can be extracted from the scattered waves' frequency spectrum. The frequency is a function of the ligament length; thus the hole depth can be obtained. The circumference of the hole is found from a time of flight measurement. A Rayleigh wave is formed that travels around the hole's surface. The length of time required for the wave to travel around the hole is a measure of the circumference.
TL;DR: In this paper, a new ultrasonic inspection method is described that permits complete volumetric inspection of the girth welds using noncontacting electromagnetic-acoustic transducers (EMATs) that operate at low ultrasonic frequencies.
Abstract: The practical implementation of alternative acceptance criteria for pipeline girth welds requires the use of inspection tools capable of determining the principal dimensions and positions of planar flaws. A new ultrasonic inspection method is described that permits complete volumetric inspection of the girth welds. The new system uses noncontacting electromagnetic-acoustic transducers (EMATs) that operate at low ultrasonic frequencies (454 kHz). Theoretical models of the measurements are developed and verified experimentally. In addition, practical performance limits of the new system are established in terms of minimum flaw sizes that can be detected. The results are related to accept-reject curves based on a model of the failure processes. An inspection protocol for field applications is also described.
TL;DR: Experimental measurements of leakage fields from cylindrical defects were obtained in a geometry which permitted simultaneous measurement of the magnetic induction of the material The results obtained are compared with calculations using a nonlinear finite difference method.
Abstract: Experimental measurements of leakage fields from cylindrical defects were obtained in a geometry which permitted simultaneous measurement of the magnetic induction of the material The results obtained are compared with calculations using a nonlinear finite difference method Both the experiments and the calculations indicate that the magnitude of the leakage field continues to grow nearly in proportion with the applied field well into the saturation region of the magnetic material The implications for magnetic particle inspection are discussed
TL;DR: In this paper, a focused acoustic source with lens axis at incident angle and point-receiver at specular reflection angle is used to obtain local interface data, which can be used to form images of local subsurface detail.
Abstract: Acoustic critical angle measurements usually involve broad beam or global isonification of a water-solid interface. In order to obtain local interface data, it is convenient to use a focused acoustic source with lens axis at incident angle θ and point-receiver at specular reflection angle θ. By scanning this combination at various critical angles (θ=θcrit), interface waves are generated locally near the lens focus. These waves penetrate the solid to a depth of approximately one shear wavelength λT and are modulated by discontinuities such as flaws, inclusions, and debonds that may be present there. A radiated longitudinal wave in water accompanies these modulated interface waves and carries information on subsurface flaws to the point-detector along the direction of a specularly reflected wave. By scanning the focus-receiver combination along the interface, the receiver output may be used to form images of local subsurface detail. We show that in anisotropic materials, such as crystals, there are generally two different θcrit where a radiating interface wave provides subsurface information. We also discuss special problems associated with the use of a focused acoustic source including nonlinear effects (generation of harmonics) in the water.
TL;DR: In this article, a method for measuring the probe area is given, and the quality of the probe is thereby characterized by two voltage measurements taken on an artificial rectangular flaw machined in an arbitrary metal.
Abstract: In the ac field method of crack depth measurement by the Crack Microgauge, the area of the loop formed in the probe gives rise to an induced voltage, which can introduce errors into the depth measurement. In this paper, a method for measuring the probe area is given, and the quality of the probe is thereby characterized. The underlying theory was given previously, and it is applied here to the probe characterization problem. The probe area is determined by two voltage measurements taken on an artificial rectangular flaw machined in an arbitrary metal. By measurements on several such specimens with the same probe, it is confirmed that the area so obtained is a characteristic of the probe and is independent of the specimen material. Thereafter, measurements on various rectangular flaws with probes of different characteristic area were taken, and very good agreement between predicted and real depths was achieved. Both theory and experiments show that probe characterization is of particular importance when this method is used to measure surface crack depths in metals of low permeability such as aluminum.
TL;DR: The radiographic response to a two-dimensional wedge-shaped object is shown to possess several properties which enable the identification of the wedge corner on the image, thereby alleviating the need for image enhancement techniques.
Abstract: Two-dimensional imaging properties of locally isotropic and isoplanatic point spread functions are described in a general radiographic context. In particular, the radiographic response to a two-dimensional wedge-shaped object is shown to possess several properties which enable the identification of the wedge corner on the image, thereby alleviating the need for image enhancement techniques. Extensions to the location of flat-edged boundaries are also discussed. The potential dimensioning application of this analysis lies in the precise and objective location of points of interest on radiographs of more complex two-dimensional objects.
TL;DR: In this paper, an adhesive layer by which a piezoceramic foil is attached to an aluminum membrane for telephone application, is examined in a nondestructive way by thermal waves.
Abstract: An adhesive layer, by which a piezoceramic foil is attached to an aluminum membrane for telephone application, is examined in a nondestructive way by thermal waves. The basic principles of the method are outlined, and its detecting power is demonstrated by evaluation of a well-defined delamination.
TL;DR: In this article, a code for the calculation of linear acoustic wave propagation in homogeneous fluid and solid materials has been derived from the thermal-hydraulics code STEALTH, which uses finite-difference techniques in a two-dimensional mesh made up of arbitrarily shaped quadrilaterals.
Abstract: A computer code for the calculation of linear acoustic wave propagation in homogeneous fluid and solid materials has been derived from the thermal-hydraulics code STEALTH. The code uses finite-difference techniques in a two-dimensional mesh made up of arbitrarily shaped quadrilaterals. Problems with two-dimensional plane strain or two-dimensional axial symmetries can be solved. Free, fixed, or stressed boundaries can be used. Transducers can be modeled by time dependent boundary conditions or by moving pistons. This paper gives a brief description of the method and shows the results of the calculation of the near fields of circular flat and focused transducers. These results agree with analytic theory along the axis of symmetry and with other codes that use a Huygens reconstruction technique off-axis.
TL;DR: In this article, the authors present results of measurements and calculations on scattering of ultrasonic waves by a solid spherical inclusion (tungsten carbide) embedded in titanium alloy by the diffusion bonding process.
Abstract: This paper, as part of a series on elastic wave scattering, presents results of measurements and calculations on scattering of ultrasonic waves by a solid spherical inclusion (tungsten carbide) embedded in titanium alloy by the diffusion bonding process. Both direct scattering and mode-converted scattering angular distributions are reported for shear and compressional incident waves. The consequences upon the signals when transmitter and receiver were interchanged are explored in a reciprocity rule.
TL;DR: In this paper, a method is described to determine the direction of vibration of ordinary ultrasonic transducers which emit transverse waves perpendicularly into the specimen, which is of great importance for the determination of the elements of the elasticity tensor of anisotropic materials.
Abstract: A method is described to determine the direction of vibration of ordinary ultrasonic transducers which emit transverse waves perpendicularly into the specimen. This knowledge is of great importance for the determination of the elements of the elasticityc tensor of anisotropic materials. In addition, a pulse echo method is described for accurate measurements of sound wave velocities in the material. This method is applied to a monocrystal made of pure copper.
TL;DR: In this paper, the effects of grain size on the non-destructive detection of surface cracks which might arise from closure stress and path irregularity variables were evaluated using an acoustic harmonic generation technique, and it was discovered that the major source of harmonic signals was grain sized crystallographic cracks.
Abstract: Alloy grain size is known to influence both the propagation path and the closure stress of surface fatigue cracks in many alloys. The general trend is for the path to be more tortuous and the closure stress to be larger, the larger the grain size. By use of Ti Al-4V and Al 7075-T6, the effects of grain size on the nondestructive detection of surface cracks which might arise from closure stress and path irregularity variables were evaluated. Titanium specimens were inspected using an acoustic harmonic generation technique, and it was discovered that the major source of harmonic signals was grain sized crystallographic cracks. Harmonic signals were larger during fatigue in an 8-µm compared to a 4-µm grain sized alloy, as there were more grain sized cracks in the large grain material. Crack closure was found to be extremely important in determining the reflected acoustic amplitude obtained in inspecting small (100–1000 µm) cracks in Al 7075-T6 using a critical angle technique. Average received amplitudes were an order of magnitude smaller for cracks at zero load than for those opened by a tensile stress. The scatter in the reflected amplitude was also large, apparently as the result of variations in the degree of the closure from crack to crack. For the 7075 material, the important effect of larger grain size was to increase the irregularity of the crack path, making the small cracks more visible acoustically at azimuthal angles not normal to the crack plane.
TL;DR: In this paper, the relationship between characteristics of elastic defects and nonspecular features of bounded ultrasonic beams reflected at the Rayleigh angle from a liquid-solid interface is investigated.
Abstract: The relationships between characteristics of elastic defects and nonspecular features of bounded ultrasonic beams reflected at the Rayleigh angle from a liquid-solid interface are investigated. The results can serve as a theoretical basis for interpretation of Rayleigh angle nonspecularly reflected beam profiles as characterization of localized surface elastic defects.
TL;DR: In this paper, the gamma-ray spectrum was observed to change as a function of the type of the jades, and the counting ratio of the photopeaks from the two most prominent constituent elements varies greatly.
Abstract: Fourteen MeV neutron activation of jades was used to test the authenticity of jades: to ascertain whether they are genuine jadeite and whether their greenish colour is genuine, both of which are important criteria for the high market value of jadeite. For given activation and measurement conditions of the jades, the gamma-ray spectrum was observed to change as a function of the type of the jades; the counting ratio of the photopeaks from the two most prominent constituent elements varies greatly as a function of the type of the jades. The ratio of counts for the Compton edges of the 1.779 MeV gamma-ray of28Al, from28Si(n,p)28Al reaction, and the 1.434 MeV gamma-ray of52V, from52Cr(n,p)52V reaction, varied as a function of the type of the jades and also as a function of the color. These results can be applied for a fast and nondestructive evaluation of jades.
TL;DR: In this paper, a new electromagnetic acoustic transducer (EMAT) is developed that measures velocities and absolute surface displacements in-plane and plane-normal to the direction of wave propagation.
Abstract: A new electromagnetic acoustic transducer (EMAT) is developed that measures velocities and absolute surface displacements in-plane and plane-normal to the direction of wave propagation. This transducer is flexible in shape and design to conform with irregular surfaces and has unique characteristics of nonresonant frequency response. Tests show that the sensitivity of this EMAT can be increased by increasing the applied magnetic field. Because this transducer is mode selective and nonresonent, its response can be related uniquely to the wave motion. This property is highly desirable for research purposes, though generally not wanted in field monitoring situations.