Showing papers on "Ultrasonic testing published in 1997"

Dynamic rock mechanics testing for optimized fracture designs

Abstract: To optimize fracture designs, rock mechanics data are needed at multiple locations in the formation and adjacent zones. This paper will review a laboratory technique that reduces testing time and cost by 60 to 80%. The technique has been successfully used on a wide variety of core and also reduces core-size requirements. Ultrasonic (dynamic) test equipment and procedures are discussed to standardize the method for petroleum industry applications and provide reliable data for fracture designs. The primary data provided are Young's modulus and Poisson's ratio. Dynamic testing has been performed on 600 cores from about 60 formations. The data are also compared to static uniaxial and triaxial data on the same cores to determine correlation coefficients between the static and dynamic data. Procedures and apparatus for performing ultrasonic testing have been successfully developed that determine the dynamic Young's moduli for weakly consolidated cores, with Young's moduli of 60 thousand psi, to hard limestone with Young's moduli of 14 million psi. Several equations are also provided that have applications to sonic logging for mechanical property evaluation of formations. The same equipment has been used to determine fracture azimuth from oriented core at significant cost savings over other techniques. The paper will also review the relative importance of rock mechanics data on optimized fracture designs.

Ultrasonic backscattering in duplex microstructures: Theory and application to titanium alloys

Abstract: A theory is presented for the ultrasonic backscattering in duplex microstructures. Assuming single scattering described by the Born approximation, we consider a microstructure consisting of macrograins containing colonies with crystallographically related orientations. General results are presented for the backscattering coefficient, assuming that all variants occur with equal probability. These are then applied to the particular case of titanium alloys, in which the macrograins are taken to be prior beta grains and the colonies are assumed to be alpha phase produced by a martensitic transformation. Numerical results illustrate the effects of ultrasonic frequency, colony size and ellipticity, and macrograin size and ellipticity on the backscattering.

Blind deconvolution of ultrasonic signals in nondestructive testing applications

Abstract: Advanced nondestructive testing techniques use a laser to generate ultrasonic waves at the surface of a test material. An air-coupled transducer receives the ultrasound that is the convolution of the signal leaving the test material and the distortion function. Blind deconvolution methods are applied to estimate the signal leaving the material.

Ultrasonic scanning apparatus for nondestructive site characterization of structures using a planar based acoustic transmitter and receiver in a rolling pond

Abstract: The invention is a carriage type sonic or ultrasonic testing apparatus for flaw and deterioration detection testing in a structure, especially concrete. The apparatus detects both location and type of flaw in a structure. The carriage unit incorporates a rolling pond feature which includes: i) foam-covered tracks and rollers, this soft foam material in addition to its primary function prevents vibration of the transducers while traversing rough surfaces such as weathered concrete. The tracks and rollers form a water-tight seal with each other and the specimen surface; ii) an air-removal brush assembly which maintains contact with a specimen surface to facilitate transmission and reception of ultrasonic energy into and out of a test specimen; iii) an ultrasonic isolator element and optional wave absorbers; and iv) the ultrasonic transducer suspension system. A transducer water bed is continuously maintained while the system is in motion across the concrete. A sealed space surrounds the transducer system, and that space is continuously flooded with water so as to keep the bottom sections of the transducers submerged. This sealed space continuously transports a sufficient amount of fluid (water) along the concrete surface for proper acoustic coupling. The ultrasonic transducer includes a granite wedge as an impedance-matching transducer faceplate material for concrete structural examinations.

Gas-coupled laser acoustic detection

Abstract: The investigation, development and application of a laser-based ultrasonic inspection system to the problems of evaluating polymer/graphite composite materials has been realized. The use of lasers to generate and detect ultrasonic waveforms in materials provides a means to detect material properties remotely. The study consisted of three main aspects: 1) A confocal Fabry-Perot (CFP) based system has been devolved which uses light reflected from the CFP interferometer to derive the ultrasonic signal. This allows higher frequency components of the detected waveforms to be discerned when compared to a CFP-based system using light transmitted through the CFP interferometer. 2) Thermoelastic and ablative laser generation of acoustic pulses in polymer/graphite composite materials has been investigated. Thermoelastic generation of ultrasound occurs when thermal energy deposited by a pulsed laser creates a localized expansion in the material. Ablative generation of ultrasound results from the creation of a plasma above the surface when the laser pulse surpasses an intensity threshold. 3) A novel technique, designated Gas-Coupled Laser Acoustic Detection (GCLAD), has been realized, in which the ultrasonic wave is detected optically after it has been transmitted from sample to air. This technique has the advantage of being independent of surface reflectivity and optical smoothness, and has comparable sensitivity to the CFP-based system.

Method of and an apparatus for detecting, identifying and recording the location of defects in a railway rail

Abstract: Method and apparatus for ultrasonic inspection of an object. A tire is mounted for rolling along the surface of the object. It contains a liquid and a transducer assembly. The transducer assembly is positioned in the tire adjacent a portion of the surface of the tire in contact with the object. The liquid and the surface of the tire in contact with the object provide an acoustic bridge between the transducer assembly and the object. An electric signal processing system is connected to the transducer assembly. It generates electric signals which are converted to acoustic signals in the transducer assembly to place acoustic signals in the object. Acoustic signals returned from the object are converted to electric signals by the transducer assembly, and are processed in the electric signal processing system to indicate flaws in the object.

A model of ultrasonic nondestructive testing for internal and subsurface cracks

Abstract: The scattering of elastic waves in a half-space containing a striplike crack is investigated. As a special case it seems that the crack may be surface breaking. A surface integral equation with the half-space Green tensor is employed. The key point of the method is the expansion of the Green tensor in Fourier representations with the free part of the Green tensor expanded in the crack coordinate system and the half-space part in the half-space coordinate system. The integral equation is discretized by expanding the crack opening displacement in terms of Chebyshew functions having the correct square root behavior along the crack edges. The incident field is emitted from an ultrasonic probe and a recent model for this is employed. The signal response in another (or the same) probe is modeled by a reciprocity argument and the stationary phase approximation is employed to simplify the final answer, which is thus only valid in the far field of the probes (yielding essentially a spherical wave). Numerical results are given and are compared with both other methods and with available experiments.

Noncontact measurement of ultrasonic attenuation during rotating fatigue test of steel

Abstract: Acoustic resonance technique has been applied to monitor the fatigue damage process of steel pipes exposed to rotating bending fatigue. The technique incorporates a superheterodyne spectrometer and an electromagnetic acoustic transducer (EMAT). The EMAT was newly developed for this purpose, and uses the magnetostrictive mechanism of ferromagnetic metals and excites and detects axial shear waves traveling around the sample pipe with axial polarization. Noncontact ultrasonic spectroscopy permits the accurate determination of the resonant frequency and the attenuation coefficient throughout the fatigue life. The attenuation coefficient shows a sharp peak around 80%–90% of the life. The evolution is interpreted as reflecting dislocation multiplication, depinning, and formation of cell structures, which is supported by transmission electron microscopy observations.

Axisymmetric Guided Wave Scattering by Cracks in Welded Steel Pipes

Abstract: Scattering of axisymmetric guided waves by cracks and weldments of anisotropic bonding material in welded steel pipes is investigated in this paper by a hybrid method employing finite element and modal representation techniques. The study is motivated by the need to develop a quantitative ultrasonic technique to distinguish flaws and bonding materials in welded cylindrical structures. Numerical results for reflection coefficients are presented for a steel pipe with cracks and V-shaped weldments with and without cracks at the interface between the weldment and the steel pipe. It is shown that as the frequency increases, the coefficients of reflection exhibit resonant peaks at the cutoff frequencies of higher guided modes. These peaks become increasingly pronounced as the slope and the length of the crack increase. Numerical results presented have important applications in quantitative nondestructive evaluation.

Development and application of ultrasonic surgical instruments

Abstract: A new approach for designing ultrasonic surgical instruments (USI) is presented. These medical instruments convert an ultrasonic signal into a mechanical vibration by utilizing a magnetostrictive method and have been found to be very useful for various medical procedures. The implemented system consists of an ultrasonic generator, a transducer, and waveguide instruments. The generator produces a high-current ultrasonic signal. The transducer converts this signal into a mechanical vibration. By use of the waveguide instrument, the vibration can be propagated and amplified. This new type of USI possesses a comprehensive ability to stop bleeding, cut bone tissues, regulate frequency automatically, control temperature, etc. The results from animal experiments and from human clinical operations show that the developed USI has the advantages in various aspects over the conventional equipment.

Ultrasonic sensor for liquid-level inspection in bottles

Abstract: In this paper, the development of a precise and dynamic ultrasonic distance sensor to measure the level of liquid in bottles for an industrial line is described. For this application, optical, capacitive or mechanical means are not suitable. In the first part the limitations of a conventional pulse-echo ranging system are discussed. A strategy to measure the time of flight based on the envelope of the echo signal is performed, solving in a practical way the problem of the complex signal reflected from the main surface, meniscus and internal walls of the bottleneck.

Ultrasonic bolt gage

Abstract: An ultrasonic bolt gage is described which uses a cross-correlation algorithm to determine a tension applied to a fastener, such as a bolt. The cross-correlation analysis is preferably performed using a processor operating on a series of captured ultrasonic echo waveforms. The ultrasonic bolt gage is further described as using the captured ultrasonic echo waveforms to perform additional modes of analysis, such as feature recognition. Multiple tension data outputs, therefore, can be obtained from a single data acquisition for increased measurement reliability. In addition, one embodiment of the gage has been described as multi-channel, having a multiplexer for performing a tension analysis on one of a plurality of bolts.

The schlieren image of two-dimensional ultrasonic fields and cavity resonances

Abstract: The schlieren technique can be used to visualize the two-dimensional ultrasonic standing wave fields associated with circular cylindrical shells under resonance conditions. However, the interpretation of the schlieren image is not simple due to the complex relationship between the acoustic and optical fields. A model for predicting the optical image in an ideal schlieren system is presented and used to investigate the influence of the acoustic pressure and optical spatial filtering on the resultant image, demonstrating the conditions under which the image is a meaningful representation of the acoustic wave field. A low-frequency (>100 kHz), wide-aperture, laboratory schlieren system is used to image the fluid column resonances of a circular cylindrical shell. Experimental results agree well with the predictions, validating the theory. Although the schlieren image is two-dimensional, limiting investigations to targets having translational symmetry, the technique is noninvasive and can potentially provide greater insight into the acoustic resonance behavior of more complex scattering geometries.

Elastic guided waves in plates with surface roughness. I. Model calculation

Abstract: This paper reports analytical research on the effect of surface roughness on ultrasonic guided waves in plates. The theoretical model is constructed by exploiting the phase-screen assumption that takes advantage of the Kirchhoff approximation, where, on a local scale, the roughness degrades only the signal phase. The effect of the rough surface on the guided wave is treated by decomposing the wave modes into their constituent partial waves and considering individually the effect of the roughness on the partial wave components as they reflect from the plate surfaces. An approximate dispersion relation is derived for the traction-free rough waveguide that is formally identical to the conventional Lamb wave equation, but incorporating the roughness parameter as a complex plate thickness. A more accurate version of the model calculation is generalized to fluid-immersed plates having only a single rough surface either on the same, or opposite, side of the plate as the incident ultrasonic field. Calculations of the reflection coefficients in the presence of roughness serve to illustrate the phenomena for the case of the guided waves.

Pitch-catch only ultrasonic fluid densitometer

Abstract: The present invention is an ultrasonic fluid densitometer that uses a material wedge and pitch-catch only ultrasonic transducers for transmitting and receiving ultrasonic signals internally reflected within the material wedge. Density of a fluid is determined by immersing the wedge into the fluid and measuring reflection of ultrasound at the wedge-fluid interface.

Field characterization of an air-coupled micromachined ultrasonic capacitance transducer

Abstract: Investigations into the field characteristics of an air-coupled ultrasonic capacitance transducer have been performed for a range of transducer configurations. The field of a 2-MHz bandwidth silicon backplate capacitance transducer has been scanned in air using a 1-mm-diam miniature detector at frequencies of up to 1.5 MHz. The radiated peak sound-pressure field is compared to theory based on a plane piston approach for various driving signals, namely pulsed and tone burst excitation. Aperture modifications, such as an annulus and a zone plate, have also been investigated and the devices have been shown to behave as predicted by theory.

Apparatus and method for ultrasonic inspection of rotating machinery while the machinery is in operation

Abstract: An ultrasonic stroboscope is used to inspect an object rotating at a first frequency to determine if the rotating object has any defects. The ultrasonic stroboscope includes a first acoustic transducer spaced apart from the rotating object. The first transducer is configured to radiate ultrasonic energy at the rotating object at a second frequency. The second frequency is substantially related to a sub-harmonic of the first frequency so that the rotating object appears acoustically substantially still. A second acoustic transducer is used to sense a reflection of the ultrasonic energy from a defect in the rotating object. The second transducer translates the sensed reflection into at least one reflection signal. A user interface is coupled to the reflection signal.

Compact ultrasonic calibration block

Abstract: An ultrasonic test standard is formed by a metal block having a unique shape incorporating an arcuate surface and a series of reflectors that enable discreet instrument measurement verifications in a relatively small area. This calibration block, though relatively small and light in weight, will perform all of the functions of a standard IIW (International Institute of Welding) type block and additional functions.

Flexible Interdigital PVDF Lamb Wave Transducers for the Development of Smart Structures

Abstract: Conventional ultrasonic or eddy current inspection of structures requires a probe to be scanned over the whole area to be tested. This is extremely time consuming, and hence costly, when large areas such as aircraft wings or pressure vessels are to be covered. A further disadvantage of ultrasonic inspection is that a coupling fluid between the transducer and the structure is generally required. The most reliable coupling method is to use immersion, the testpiece being fully immersed in a water bath. However, with large structures this is frequently not practical and they are often tested using jet probe assemblies, the ultrasound being propagated down jets of water directed at the structure. However, this is generally only practical at the manufacture stage and field inspection is often carried out manually using contact transducers, coupling being achieved by applying gel to the surface of the structure. Many structures also have critical areas which are difficult to inspect because access is impeded. For example, spars and other stiffeners in aircraft pose problems because once the aircraft is built they are covered by the fuselage or wing skin.

Determination of grain-size distribution from ultrasonic attenuation: Transformation and inversion

Abstract: Although researchers often describe a particular medium with only a single grain size or an average grain size, distributions of grain sizes can have significant effects on the physical characteristics of the material. Ultrasonic attenuation due to energy scattered at the grain boundaries depends on the ultrasonic wavelength, the grain size, and certain material properties such as elastic constants. This paper examines the relationship between the wavelength dependency of ultrasonic attenuation and grain-size distributions. A transformation is developed which solves a general class of Fredholm equations of the first kind. The equation relating attenuation to grain-size distributions belongs to this class of equations. The transformation allows attenuation to be calculated by discrete convolution, and provides a method for estimating the grain-size distribution directly from attenuation measurements.

Method and apparatus for ultrasonic testing of aluminum billet

Abstract: An ultrasonic inspection apparatus and method tests elongated, cylindrical aluminum billets. The apparatus includes a frame supporting a movable carriage having at least one ultrasonic detector assembly mounted thereon. Each ultrasonic detector assembly includes a bracket detachably mounted to the carriage, at least one holder movably coupled to the bracket, a spring-biasing mechanism to bias the holder from the bracket, a transducer shoe attached to the holder and a transducer attached to the shoe. The shoe is configured to conform to the outer surface of the billet and to be flooded with fluid to assist in testing.

Lamb wave ultrasonic probe for crack detection and measurement in thin-walled tubing

Abstract: A probe inspects steam generator tubing for defects. The probe includes a transducer which generates a localized ultrasonic Lamb wave. The ultrasonic wave is transferred to the tubing by a coupling medium, such as water, that physically couples the transducer and the tubing. Defects in the tubing reflect the ultrasonic wave to the probe which detects the reflections. The results are thenused to determine the length and depth of such defects as cracks, pitting, and thinning. The localized ultrasonic wave performs and inspection sensitive enough to detect ligaments between crack segments. This allows highly accurate predictions of tubing integrity and rupture strength.

Nondestructive evaluation (NDE) of composite-to-metal bond interface of a wind turbine blade using an acousto-ultrasonic technique

Abstract: An acousto-ultrasonic inspection technique was developed to evaluate the structural integrity of the epoxy bond interface between a metal insert and the fiber glass epoxy composite of a wind turbine blade. Data was generated manually as well as with a PC based data acquisition and display system. C-scan imaging using a portable ultrasonic scanning system provided an area mapping of the delamination or disbond due to fatigue testing and normal field operation conditions of the turbine blade. Comparison of the inspection data with a destructive visual examination of the bond interface to determine the extent of the disbond showed good agreement between the acousto-ultrasonic inspection data and the visual data.

Observation and Interpretation of Microstructurally Induced Fluctuations of Back-Surface Signals and Ultrasonic Attenuation in Titanium Alloys

Abstract: During ultrasonic inspection for flaws in engineering materials, it is important to understand the interactions between the inspecting beam and the microstructure in which flaws are embedded. It has been found that in certain materials such interactions can have dramatic effects on the characteristics of the beam as it propagates to and from a flaw and consequently can have deleterious effects on both flaw characterization and the probability of detection. It is well known that, the microstructure can backscatter energy, creating noise which can mask small flaws. In addition, a flaw signal can be attenuated by the removal of energy from the beam by absorption and scattering. Considerable progress has been made towards developing a theoretical understanding of these phenomena. For example, backscattered grain noise has been successfully modeled by Han and Thompson [1] for duplex microstructures that commonly occur in Ti-17 and Ti-6A1-4V alloys used in the rotating components of aircraft engines. In addition, attenuation has been modeled for randomly oriented, equiaxed, cubic microstructures [2], for textured, equiaxed, cubic, stainless-steel [3], and also for elongated textured microstructures [4].

The use of large ultrasonic transducers to improve transmission coefficient measurements on viscoelastic anisotropic plates

Abstract: A study of the use of large transducers (80 mm×40 mm, 3.2 MHz center frequency) for the measurement of ultrasonic transmission coefficients is reported. Tests have been carried out on thick and thin glass plates and on a unidirectional carbon fiber composite plate. The material properties of the plates were obtained by comparing the transmission coefficient results at particular angles with the predictions of plane-wave theory for different material properties; the properties giving the best fit were then used to predict the transmission coefficients at other angles. The results of this preliminary study show that the use of large transducers makes it possible to obtain excellent agreement between measured transmission coefficients at all angles and those predicted using plane-wave theory. The large transducers give clearer definition of the transmission maxima than is obtained with smaller, conventional transducers, and also give good agreement with the predicted transmission coefficient amplitudes. This...

Air coupled NDE-constraints and solutions for industrial implementation

Abstract: There is increasing industrial interest in the use of non-contact, gas-coupled ultrasound for a range of non-destructive evaluation (NDE) applications. Ultrasonic generation and detection via piezoelectric or electrostatic transducers have attracted particular interest and a number of related publications have appeared in the recent technical literature. However, these have centred largely on laboratory experiments since extrapolation of the technology to the real industrial environment is not straightforward. Questions still remain with regard to the practical robustness and reliability of such systems. This paper addresses the major difficulties associated with industrial implementation of gas coupled NDE. The influence of the gas channel on ultrasonic wave propagation is described with regard to system operating frequency, ultrasonic beam characteristics and possible environmental variables such as temperature and pressure. Methods for predicting and stabilising ultrasonic system performance are proposed, in conjunction with transducer design, where emphasis is placed on efficiency for gas operation and the requirement for minimisation of electronic intrinsic noise. Techniques for implementing sufficient improvement to enable practical, real time operation are then discussed, including instrumentation design and signal conditioning requirements. Finally, examples of robust NDE systems are presented, embracing through transmission scanning, array based imaging and multi-frequency Lamb wave scanning.

The acoustic finite integration technique for waves of cylindrical symmetry (cafit)

Abstract: Many ultrasonic nondestructive testing applications have cylindrical geometries. Examples involve the excitation of ultrasound by cylindrical piezoelectic probes or by laser, x rays, electron beams [A. C. Tam, Rev. Mod. Phys. 58, 381–431 (1986)], or ion beams [L. Sulak et al., Nucl. Instrum. Methods 161, 203–217 (1979)]. Thus, calculations of cylindrical wave propagation are important for a better understanding and interpretation of many testing situations. This paper deals with the AFIT Code or finite volume method for numerical simulation of sound propagation in fluids adapted to cylindrical geometries (CAFIT). A comparison is made with standard difference-equations techniques also utilized for cylindrical geometries. Two examples are dealt with: (1) The sound generation by a high energy beam of heavy ions stopping in water; (2) the multimode sound propagation in a medical doppler injection device excited by a disk probe.

Laser generation and detection of ultrasound in concrete

Abstract: Laser ultrasonic techniques are used to examine the propagation of ultrasonic waves in concrete. This optical methodology provides a repeatable, broad band generation source and an absolute detection system that does not interfere with the process being monitored. The presence of aggregate, in addition to voids and flaws, can cause wave scattering in concrete. Fast Fourier Transform techniques are used to determine the effect of aggregate size and propagation distance on the frequency content of both surface and body waves. This paper examines the scattering of ultrasonic waves in undamaged concrete and establishes the fundamentals for the application of laser ultrasonics for the material characterization and nondestructive evaluation of concrete.