Showing papers on "Ultrasonic testing published in 1984"

Reconstruction of inclusions in solids using ultrasonic Born inversion

Abstract: Voids and inclusions in elastic solids are characterized experimentally using scattered ultrasonic waves The flaws are reconstructed using a one‐dimensional elastic wave inverse scattering algorithm based on the Born–Neuman expansion This method emphasizes the role of low and intermediate frequency longitudinal waves The utility of the inverse Born approximation is tested for several new circumstances First the algorithm is tested for pitch‐catch (bistatic) geometries Secondly the effects of resonant excitation of the scatterer on flaw characterization are measured for several spherical flaws The third and major result shows that the one‐dimensional algorithm can be used to determine the size, shape and orientation of nearly ellipsoidal flaws when access angle is limited The effects of varying access aperture on the reconstruction are reported Another common experimental limitation in flaw characterization arises from interferences of the flaw signal with nearby surfaces We briefly report that th

Multibeam satellite-pulse observation technique for characterizing cracks in bimetallic coarse-grained component

Abstract: Ultrasonic testing methods and units for characterizing planar flaws in hard-to-inspect materials such as welded and cladded pipes containing intergranular stress corrosion cracks. The invention characterizes flaws with pitch-catch transducers positioned front to back on a single module. One module uses a bimodal transducer to transmit longitudinal and shear waves to produce, through surface wave mode conversion, reflection and diffraction, a triplet of associated longitudinal and shear wave signals received by another bimodal transducer. Other modules use pitch-catch transducers to produce a doublet of associated shear wave signals from diffraction of an incident longitudinal and/or shear waves at the upper and lower extremities of underclad fatigue cracks and buried cracks. The signals are enchanced by multiple one sided cross focusing on preselected target areas in the test specimen and are cognizable by pattern recognition. Flaw characterization results from the created linear relationship between signal separation and crack depth.

Laser-based non-destructive testing techniques for the ultrasonic characterization of subsurface flaws

Abstract: Laser generation and detection of ultrasound has been used for remote characterization of flat-bottomed holes, acting as subsurface flaws, drilled into an aluminium test sample. A pulsed Nd:YAG laser system was used to generate the ultrasonic source whilst a HeNe laser interferometer detected the subsequent surface displacements. The technique allows both the width and depth of flawa to be assessed. Moreover, an analysis of the data shows that the method is particularly suited to detection of flaws ≤ 4 mm below the surface of the sample, a region which is difficult to inspect by conventional contact ultrasonic techniques.

Ultrasonic wave propagation characteristics of green ceramics

Abstract: Propagation of ultrasonic waves in green (unfired) ceramics is studied, and the effectiveness of ultrasonic methods for nondestructive evaluation is assessed. The objective is to obtain useful information on defects, cracking, delaminations, agglomerates, inclusions, regions of high porosity, and anisotropy. Conventional ultrasonic techniques are difficult to apply to flaw detection in green ceramics because of the high attenuation, fragility, and couplant-absorbing properties of these materials. However, velocity, attenuation, and spectral data were obtained with pressure-coupled transducers and provided useful information related to density variations and the presence of agglomerates and elastic anisotropy.

Review and discussion of the development of synthetic aperture focusing technique for ultrasonic testing (SAFT-UT)

Abstract: The development and capabilities of synthetic aperture focusing techniques for ultrasonic testing (SAFT-UT) are presented. The purpose of SAFT-UT is to produce high-resolution images of the interior of opaque objects. The goal of this work is to develop and implement methods which can be used to detect and to quantify the extent of defects and cracks in critical components of nuclear reactors (pressure vessels, primary piping systems, and nozzles). This report places particular emphasis upon the practical experimental results that have been obtained using SAFT-UT as well as the theoretical background that underlies synthetic aperture focusing. A discussion regarding high-speed and real-time implementations of two- and three-dimensional synthetic aperture focusing is also presented.

Ultrasonic microscope system

Abstract: An ultrasonic transmitter-receiver (16) for radiating a focused ultrasonic beam (39) and a sample (23) are moved relative to each other in the axial direction of the ultrasonic beam. A reflected wave from the sample (23) is received and a curve V(Z) of variations in the level of the reflected wave with respect to the relative movement is obtained. A reference level of interference of a directly reflected wave and a leaky elastic wave is substracted from V(Z) to perform waveform processing. The waveform processing output is subjected to a waveform analysis, and from the analysis results, the velocity and/or the attenuation of the leaky elastic wave are calculated.

Ultrasonic inspection system

Abstract: An ultrasonic inspection system for inspecting areas of tubular members and providing a display of any internal flaws therein. In order to operate in a confined work space a probe containing ultrasonic transducers is provided together with a rotational and axial drive scanner which is linked to a remotely controlled manipulator. The scanner uses a wand supporting the probe at the upper end thereof. The manipulator locates the probe and scanner in alignment with the tube to be inspected. A stepping motor on the scanner drives the wand and the probe axially to a location just above the area to be inspected. A second stepping motor rotates the wand to enable the probe to perform a circumferential scan. The axial stepping motor then indexes the wand towards the lower edge of the area and another circumferential scan occurs. The indexing and circumferential scanning proceeds until the entire area is scanned. The signals received from the ultrasonic transducers are digitized and processed, with the aid of programmed digital computer, so as to graphically display the interior interface of the sleeve and tube which is scanned to show any voids as may be due to incomplete bonding between the sleeve and the tube.

Absolute Measurements of Ultrasonic Attenuation Using Damped Nondestructive Testing Transducers

Abstract: This paper reviews the method for making absolute ultrasonic attenuation measurements by means of nondestructive testing transducers and liquid buffer columns or solid buffer rods. The principle is that the transducer must be separated from the specimen so that the transducer cannot influence the echoes in the specimen. Then the attenuation coefficient in the specimen and the reflection coefficient at the buffer/specimen interface can be calculated from the amplitudes of the first three echoes in the buffer/specimen system. For absolute measurements, the amplitudes must be corrected for ultrasonic beam spreading (diffraction). The theory of the measurements and the corrections is recapitulated, and experimental examples are given showing the utility of the method. Experimental techniques are also recapitulated.

Ultrasonic detection of molten/solid interfaces of weld pools

Abstract: Ultrasonic techniques are being studied for the detection and location of the liquid/solid interfaces of molten weld pools in metals during the welding process The objective of the study is to develop a technique for sensing the depth or lateral position of a weld pool and providing a real-time control signal to the welder to achieve a completely automated, process-controlled welding system Experimental results illustrating the feasibility and limitations of the technique are presented 10 references

Measurement of small elastic anisotropy in solids using laser-induced ultrasonic pulses

Abstract: Nondestructive laser‐induced short ultrasonic pulse generation (duration ≊10 ns) together with broadband detection is used to detect and measure the small elastic anisotropy in opaque solids quickly and precisely. This is demonstrated for an extruded aluminum alloy type 6061‐T6. A single laser‐induced acoustic pulse propagation measurement over a path length of 47 mm provides a longitudinal ultrasonic velocity measurement accuracy of 0.02%. The longitudinal velocities at ±45° from the extruding direction Z are found to be 2% larger than the velocity along Z, indicating that most of the aluminum crystallites are oriented with a principal axis parallel to Z. Thermal annealing of the sample results in a small increase in ultrasonic veolcity in all directions with the observed acoustic anisotropy remaining essentially unchanged.

Measurement of the thickness of thin layers by ultrasonic interferometry

Abstract: An ultrasonic interferometer working in a pulsed mode is described in this paper. It allows for the measurement of coating thicknesses as thin as 5 μm with a 5% precision over different substrates at a very high rate (up to 1000 times per second). The optimal conditions for this interferometric measurement are defined theoretically and the probe characteristics have been optimized technologically. This, together with the design of a very large frequency bandwidth (from 90 to 510 MHz) electronic setup, leads to interesting performances. The advantages of the system for achieving thickness measurements are discussed and comparisons are made with other systems.

Wide Band Ultrasonic Transducer Using Tapered Piezoelectric Ceramics for Non-Destructive Inspection

Abstract: The purpose of this paper is to develop a new ultrasonic transducer for non- destructive inspection composed of tapered piezoelectric ceramics in longitudinal or shear mode. Some experimental results on the transducer are presented. The result obtained is that the transducer can be fabricated easily without backing treatment because the tapered piezoelectric ceramics shows multi-resonances in its vibration. The wide frequency band characteristics can therefore be realized and a narrow ultrasonic pulse signal can be radiated. The radiation direction of longitudinal ultrasonic wave generated by tapered piezoelectric ceramics in shear mode is also described.

Inference of fatigue-crack closure stresses from ultrasonic-transmission measurements

Abstract: The nondestructive determination of stress is usually attempted by measuring stress (or strain) related changes in material properties. Included are direct x-ray measurements of lattice constants and indirect inferences of stress or strain from changes in ultrasonic velocities or magnetic properties. However, in problems in which one wishes to determine localized stresses across an interface between two materials, neither approach is satisfactory. X-rays typically measure surface stresses and do not sample the stress condition near an internal interface. Ultrasonic velocity measurements and magnetic measurements can sense interior conditions, but also average over the properties of the intervening material. Hence, they cannot determine the localized stresses at the interface without sophisticated data reduction techniques such as those employed in holographic reconstructions.

Mode-conversion ultrasonic testing.

Abstract: The review presents background to the mode conversion and total wave techniques and a model for describing the new techniques. The results are applied to surface crack sizing, body defect sizing and imaging. New forms of inspection using leaky Rayleigh waves for surface crack detection and characterization are also considered. The complete system of data obtained can be evaluated in terms of fracture mechanics and failure models.

New transducers for high-resolution ultrasonic testing

Abstract: High resolution NDT requires ultrasonic transducers which can produce very short pulses with well-defined constant shape throughout the field. The theory, construction and applications of such transducers are discussed.

Review of progress in quantitative nondestructive evaluation. Vol. 3B

Abstract: This two-book volume constitutes the Proceedings of the Tenth Annual Review of Progress in Quantitative Nondestructive Evaluation held in California in 1983. Topics considered include nondestructive evaluation (NDE) reliability, ultrasonics (probability of detection, scattering, sizing, transducers, signal processing, imaging and reconstruction), eddy currents (probability of detection, modeling, sizing, probes), acoustic emission, thermal wave imaging, optical techniques, new techniques (e.g., maximum entropy reconstruction, near-surface inspection of flaws using bulk ultrasonic waves, inversion and reconstruction), composite materials, material properties, acoustoelasticity, residual stress, and new NDE systems (e.g., retirement-for-cause procedures for gas turbine engine components, pulsed eddy current flaw detection and characterization, an ultrasonic inspection protocol for IN100 jet engine materials, electromagnetic on-line monitoring of rotating turbine-generator components). Basic research and early engineering applications are emphasized.

Ultrasonic test instrument with controllable amplifier

Abstract: The invention relates to an ultrasonic test instrument, in which a receiver amplifier is controlled in dependence upon time by means of a depth compensation signal or else the ultrasonic signal amplified independently of the depth is evaluated by means of a time-dependent variable threshold signal. The depth compensation signals and the time-dependent threshold signals are derived from the same digital signal values stored in a main memory. The test instrument comprises a microprocessor by means of which the digital signal values for each material requiring testing are automatically measured by the instrument itself in conjunction with whichever test probe is used provided a corresponding test block of this material is available. The microprocessor also controls the circuit generating the depth compensation and threshold signals, so that depending upon the type of operation selected the cathode ray tube can display either the ultrasonic echo responsive signals corrected as a function of depth or the uncorrected ultrasonic signals are shown together with the time-dependent threshold value.

Ultrasonic transducer probe for providing beams with adjustable angle

Abstract: The invention concerns an ultrasonic test probe for use in connection with testing workpieces wherein the angle of propagation of the ultrasonic search beam is adjustable. The probe comprises a linear array of ultrasonic transducer elements and a plastic wedge. An acoustic lens disposed between the array and the wedge causes the individual ultrasonic beams to come to a focus at an acoustic energy exit aperture of the probe. The angle adjustment of the ultrasonic beams is accomplished by energizing in-phase a respective group of transducer elements forming the array.

A new ultrasonic method for stress determination in textured materials

Abstract: Non-destructive measurement of stress using ultrasonics often fails because of texture in the analysed material: texture as well as stress influences the wave velocity and reliable methods are needed to separate the two effects. This contribution briefly reviews earlier approaches and presents a new method to separate texture and stress effects by measuring the velocity dispersion of polarized shear waves. The techniques is based upon recently published theoretical work on wave propagation in polycrystalline quasi-isotropic as well as textured materials. Experimental results are in general agreement with the theoretical data.

Ultrasonic shear wave couplant

Abstract: Ultrasonically testing of an article at high temperatures is accomplished by the use of a compact layer of a dry ceramic powder as a couplant in a method which involves providing an ultrasonic transducer as a probe capable of transmitting shear waves, coupling the probe to the article through a thin compact layer of a dry ceramic powder, propagating a shear wave from the probe through the ceramic powder and into the article to develop echo signals, and analyzing the echo signals to determine at least one physical characteristic of the article.

Movable ultrasonic transducer array

Abstract: @ A movable, ultrasonic transducer array for use in an ultrasonic inspection system that employs a signal detector and display of the liquid crystal cell (18) type. The movable array uniformly insonifies the object (16) to be inspected and is particularly for inspecting large objects or large areas of an object. The array includes a plurality of sending or emitting transducers (14) which are held in substantially parallel alignment so that their transmission or radiation axes are parallel. The array is part of an assembly which includes a support (24, 26) for holding the transducers and a drive system (28 to 38) for moving the array and support along a predetermined path.

Ultrasonic resonance for detecting changes in elastic properties

Abstract: Some forms of corrosion, and inter-granular attack in particular, occur without significantly altering the bulk dimensions of the body attacked. Where elastic properties are changed, this is detected by a sensitive ultrasonic inspection based upon the resonant frequency or frequencies with which the ultrasonic signals reverberate within the body. Resolution is improved by gating out the first, top, surface reflection and by swept gain control through the gating period.