Showing papers on "Ultrasonic testing published in 1996"

Ultrasonic methods of non-destructive testing

Abstract: Introduction. The propagation of low amplitude ultrasound. Ultrasonic characterization. Ultrasonic transducers. The principles of ultrasonic testing. Ultrasonic testing equipment. Ultrasonic flaw detection. Flaw sizing in metals. The testing of metals. The examination of non-metals and adhesive bonds. Training, certification and standards. Further reading. Appendices.

Ultrasonic liquid level gauge for tanks subject to movement and vibration

Abstract: One or more high-frequency ultrasonic transducers are used to measure the liquid level of tanks containing any type of fluid, but fuel in particular. The invention relates specifically to tanks that are subject to movement and vibration which generally makes the use of ultrasonic echoes unreliable for obtaining accurate level measurements. A special algorithm is used to obtain the temporal center of the distribution of echo arrival times over a preset time interval. From this temporal center of an echo distribution, the liquid level is readily obtained through the acoustic velocity, time and distance relationship. An annular piezoelectric plate, independently driven at low ultrasonic frequencies (kHz range), mounted on the tank bottom surrounds the high frequency ultrasonic transducer. The function of the piezoelectric plate is to send out propagating ultrasonic waves (essentially longitudinal) to maintain the tank area in the immediate region of the high-frequency transducer free from debris and sediment deposits at the bottom of the tank thereby avoiding the uncertainty in the measurement that is introduced by debris on the tank bottom.

Micromachined ultrasonic transducers: 11.4 MHz transmission in air and more

Abstract: The fabrication and modeling of novel, capacitive, ultrasonic air transducers is reported. Transmission experiments in air at 11.4, 9.2, and 3.1 MHz are shown to correspond with theory. The transducers are made using surface micromachining techniques, which enable the realization of center frequencies ranging from 1.8 to 11.6 MHz. The bandwidth of the transducers ranges from 5% to 20%, depending on processing parameters. Custom circuitry is able to detect 10 MHz capacitance fluctuations as small as 10−18 F, which correspond to displacements on the order of 10−3 A, in a bandwidth of 2 MHz with a signal to noise ratio of 20 dB. Such detection sensitivity is shown to yield air transducer systems capable of withstanding over 100 dB of signal attenuation, a figure of merit that has significant implications for ultrasonic imaging, nondestructive evaluation, gas flow and composition measurements, and range sensing.

Ultrasonic Measurements and Technologies

Abstract: Introduction. Ultrasonic waves. Ultrasonic transducers. Ultrasonic digital measuring methods. Non-destructive testing (NDT). Measurement of position and air flow by pulse methods. Ultrasonic Instruments: case studies. Index.

Ultrasonic inspection of long steel pipes using Lamb waves

Abstract: An ultrasonic inspection technique using Lamb waves was evaluated to detect and determine the exact location of flaws present in long steel pipes. Since multiple modes of Lamb waves are generated due to their dispersive characteristics in the inspected pipes, the selection of a specific Lamb wave mode is very important for inspection of flaws. Experimental studies of flaw detectability with the use of each Lamb wave mode, namely, the A 0 S 0 , A 1 , and S 1 modes and their ultrasonic attenuation characteristics were conducted. The experimental results showed that the A 0 mode is the most effective for detection and exact determination of the location flaws. A lucite wedge containing a water column that generates the A 0 Lamb wave mode was developed and used in the present inspection study. It was found that the ultrasonic beam divergence after wrapping around the inspected pipe once interferes with exact determination of the location of flaws and that the maximum reflection signals are obtained when the transducer is offset axially from the straight line with the position of the flaw. The present study showed feasibilities of ultrasonic inspection with the use of Lamb waves for detection of flaws in insulated or inaccessible steel pipes.

Method for real-time ultrasonic testing system

Abstract: An ultrasonic real-time inspection method which is user-friendly in an interactive environment to provide ease of operation, as well as a combination of consistency, thoroughness, and speed of operation in flaw detection not achievable by other methods. The method offers significantly increased pattern recognition capability, which provides greater automation potential and reduced missed detection and false alarm rates.

Industrial ultrasonic imaging and microscopy

Abstract: Ultrasonic imaging and scanned acoustic microscopy are terms used to describe similar imaging processes at different magnifications and frequencies. Both processes form images by acquiring spatially correlated measurements of the interaction of high-frequency sound waves with materials. With the exception of the interference measurement, called V(z), and the gigahertz frequencies used by the higher frequency scanning acoustic microscopes, it is difficult to establish operational differences between them. This is especially true since almost all commercial ultrasonic imaging systems use transducers producing focused beams and can display magnified high-resolution images. Ultrasonic C-scan imaging was developed largely by the ultrasonic nondestructive testing industry. The development was gradual and evolutionary. Over a 50-year period, better and better broadband transducers, electronics and scanners were developed for operation at progressively higher frequencies, now ranging from 1.0 to 100 MHz. Conversely, scanning acoustic microscopes made a relatively sudden appearance 20 years ago on the campus of Stanford University. The first scanning acoustic microscopes operated at gigahertz frequencies and used microwave electronics that produced acoustic tone bursts with many wavelengths per pulse. Three factors control resolution in an acoustic image: diameter of the acoustic beam or its point spread function (PSF); size and spacing of the pixels making up the image; signal-to-noise ratio (contrast) of the feature being resolved. The beam diameter, or PSF, is controlled by the frequency of the ultrasonic pulse and the focal convergence of the beam (or focal length to diameter ratio Z/d). In the coupling fluid, the Z/d ratio is determined by the transducer diameter and lens, but in the material, Z/d is established by the materials ultrasonic velocities. Pixels are the squares of colour or greyscale that make up computer displays of scanned images. Following Nyquist's criterion, the resolution of those images is twice the size and spacing of the pixels. It follows, therefore, that in order to support the resolution of an ultrasonic beam, the pixels must be no larger than half that beam diameter. Finally, the contrast of the feature being studied must be (at least) a clear shade of grey above the background produced by the image noise. The noise can be due to the material or the electronics. Written to support industrial ultrasonic inspection of materials, this discussion will emphasise the similarities between imaging and microscopy rather than the differences. The roles of the focusing lens, the pulse frequency, and the material being imaged, with respect to the final resolution of an acoustic image, will be considered in detail. It will be shown that additional improvements in resolution can be achieved with image processing. Finally, applications studies in metals, ceramics, composites, attachment methods, coatings, and electronic assemblies will be used to demonstrate specific roles for imaging/microscopy in nondestructive testing.

Ultrasonic characterization of a polymerizing epoxy resin with imbalanced stoichiometry

Abstract: The effect of the mixing ratio of curing agent to epoxy prepolymer on the isothermal polymerization of common epoxy systems has been characterized by ultrasonic spectroscopy During polymerization, changes in longitudinal ultrasonic wave properties (velocity and attenuation) were observed These changes were related to the glass transition temperature of the resins The profile of velocity and attenuation clearly depended on the mixing ratio In all resins, the wave attenuation exhibited a peak in the primary relaxation (α)

Measurement of stiffness coefficients of anisotropic materials from pointlike generation and detection of acoustic waves

Abstract: A scanned point source‐point receiver technique, based on laser generation and detection of acoustic waves, is used to measure the stiffness coefficients of anisotropic materials. The striking effects that anisotropy gives rise to are analyzed and, when possible, advantage is taken of them. The processing developed for recovering the coefficients is presented and applied starting with simulated or experimental signals. A silicon crystal, for which acoustic wave focusing induced by anisotropy is critically sensitive, is first studied. To provide an accurate interpretation of these waves, the two‐dimensional problem considering a line source is discussed, before analyzing the point source generation. Secondly, a manufactured composite material is characterized by means of this noncontact technique. By scanning a symmetry plane, four coefficients of the stiffness tensor are then recovered with good reliability.

A neural network for crack sizing trained by finite element calculations

Abstract: A neural network is combined with a self-compensating ultrasonic technique to size cracks emanating from rivet holes. The network is trained with a combination of experimental and synthetic data. A 2-D finite element (FE) method is used to generate synthetic data for scattering of ultrasound by cracks emanating from rivet holes in a thin aluminium sheet. Both the back and forward scattered fields are calculated at several positions parallel to the crack line. An experimental pulse from an ultrasonic transducer is applied as input excitation to the FE grid. The FE program generates a set of back- and forward-scattered signals for cracks of various lengths in the range; 0.25–3.00 mm with length increments of 0.25 mm. Data obtained in this way are used to train the neural network (NN) classifier that categorizes the data according to crack length. Once the network is trained, its performance is tested on self-compensated experimental data obtained by ultrasonic testing of specimens containing cracks of lengths in the range 0.50–3.00 mm with length increments of 0.50mm. The use of FE modelling to train the NN eliminates the need for a large number of experiments.

Method for ultrasonic imaging and device for performing the method

Abstract: A method for ultrasonic imaging of interior structures and flaws in a test specimen with a smooth or irregular contact surfaces, in which an ultrasonic transducer is coupled acoustically to the contact surface via a plurality of ultrasonic wave guides with equal delay times. The wave guides are thin and bendable, so they adapt to variations in the distance between the transducer and different parts of the contact surface by bending more or less. All parts of the irregular contact surface accordingly receive sound waves that are in phase, even when the contact surface is irregular, so a coherent sound wave is infused in the test specimen. The wave guides can be arranged in the form of an ultrasonic brush, with a flat head for coupling to a flat transducer, and free bristles that can be pressed against the test specimen. By bevelling the bristle ends at a suitable angle, shear mode waves can be infused into the test specimen from a longitudinal mode transducer.

Electromagnetic acoustic transducer (emat) for ultrasonic inspection of liquids in containers

Abstract: An ultrasonic inspection technique using a specially designed electromagnetic acoustic transducer (EMAT) launches and receives longitudinal ultrasonic waves into a thin metal wall or thin metal foil seal of a container, causing it to vibrate and launch ultrasonic compressional waves into liquid contained therein. The contents of plastic containers having a metal foil seal forming one wall are easily inspected. The EMAT establishes a magnetic field in the surface of the metal parallel to the surface. Radio frequency (RF) eddy currents are also induced by the EMAT in the surface of the metal. A Lorentz force is generated in the metal surface according the vector product of J, the current density, and H, the magnetic field, and the force generated by the interaction of the perpendicular components of the magnetic field H and the eddy currents J is directed normally to the surface of the metal. This normal force oscillates with the frequency of the induced eddy currents creating ultrasonic compressional waves which propagate normal to the surface of the metal. In such thin-walled metal containers or thin metal foil seals, where the thickness of the metal is much shorter than the ultrasonic wavelength in the metal, the generation and reception process is analogous to the operation of a loudspeaker in air. In this application, the thin metal wall or foil acts as a membrane, with the Lorentz forces generated in the wall or foil causing the metal membrane to vibrate, generating ultrasonic waves in the liquid. Because the thin wall or foil is much more compliant than a thick piece of metal, much larger displacements are generated at the metal-liquid interface than for the thick-wall case, resulting in much larger signal amplitudes than in the thick-wall case.

An ultrasonic sensor for high-temperature materials processing

Abstract: A sensor has been developed and tested that is capable of emitting and receiving ultrasonic energy at temperatures exceeding 900°C and pressures above 150 MPa. The sensor works with standard ultrasonic pulser-receivers and has demonstrated the capability of measuring workpiece deformation during hot isostatic pressing. Details of the sensor design, performance, and coupling of the ultrasound to the workpiece are described. Ultrasonic data acquired by the sensor in-situ during hot-isostatic-pressing runs are presented.

Flexible ultrasonic pipe inspection apparatus

Abstract: A flexible, modular ultrasonic pipe inspection apparatus, comprising a flexible, hollow shaft that carries a plurality of modules, including at least one rotatable ultrasonic transducer, a motor/gear unit, and a position/signal encoder. The modules are connected by flexible knuckle joints that allow each module of the apparatus to change its relative orientation with respect to a neighboring module, while the shaft protects electrical wiring from kinking or buckling while the apparatus moves around a tight corner. The apparatus is moved through a pipe by any suitable means, including a tether or drawstring attached to the nose or tail, differential hydraulic pressure, or a pipe pig. The rotational speed of the ultrasonic transducer and the forward velocity of the apparatus are coordinated so that the beam sweeps out the entire interior surface of the pipe, enabling the operator to accurately assess the condition of the pipe wall and determine whether or not leak-prone corrosion damage is present.

Predicting ultrasonic grain noise in polycrystals: A Monte Carlo model

Abstract: A Monte Carlo technique is described for predicting the ultrasonic noise backscattered from the microstructure of polycrystalline materials in a pulse/echo immersion inspection. Explicit results are presented for equiaxed, randomly oriented aggregates of either cubic or hexagonal crystallites. The model is then tested using measured noise signals. Average and peak noise levels and the distribution of the noise voltages are studied as the density of grains changes.

Method and apparatus for ultrasonic inspection of electronic components

Abstract: A method and apparatus for non-destructive ultrasonic inspection in which a plurality of integrated circuits or other electronic components laid out in a fixed pattern on a liquid-permeable tray are moved along an inspection path through a scanning station. In the scanning station the electronic components are repetitively scanned by an ultrasonic beam from a transmitter/receiver moving rapidly back and forth across the inspection path; an ultrasonic coupling liquid (usually water) continuously flows along the beam path; the coupling liquid also flows along the surfaces of the electronic components opposite the beam path. The tray of electronic components is air dried as it emerges from the scanning station. Both reflected and "through" ultrasonic signals can be collected to disclose any anomalies present in the electronic components. A screen may be used to assure retention of the electronic components in the desired pattern on a tray.

Ultrasonic flowmeter and ultrasonic generator/detector

Abstract: An ultrasonic flowmeter includes a flow passage and an ultrasonic generator/detector for measuring the flow rate in the flow passage wherein the ultrasonic generator/detector is equipped with a piezoelectric body having electrodes on the opposed surfaces thereof, one of which is used as an ultrasonic wave generating/detecting surface and faces the flow passage. The lengths of the sides of the generating/detecting surface is so determined that the vibration in the electrode direction is the main mode, preferably that the ratio of the lengths of the sides of the transmission/reception surface to the thickness is not greater than 0.8. Consequently, because the flow meter uses the thickness longitudinal vibration of the piezoelectric body as the main mode, the ultrasonic generator/detector has a high sensitivity, a high speed response and a small size and the ultrasonic flow meter has a high accuracy and is compact.

Flaw detection apparatus employing tire probes having ultrasonic oscillators mounted therein

Abstract: An apparatus for detecting flaws using supersonic waves measures a thickness of a test object or a position of a cavity inside the test object by employing a pair of ultrasonic probes. By, changing a relative position of one ultrasonic probe to that of the other ultrasonic probe, a plurality of waveform data of ultrasonic reception signals is acquired. Each of the acquired waveform data is added together. Because a surface wave component of each waveform data has a shifted phase due to a difference in arrival times, a level of the surface wave component is offset and thus minimized through addition of the waveform data.

Ultrasonic pulser/receiver for ultrasonic test equipment

Abstract: A configuration flexible computer-controlled ultrasonic diagnostic test equipment arrangement for examining large turbine rotors incorporates improved ultrasonic signal "pulser-receiver" circuitry that is used to drive one or more an ultrasonic transducers and to receive and amplify ultrasonic returns from a specimen under test. The improved pulser-receiver circuitry comprises both an ultrasonic pulse generating circuit and an associated ultrasonic return signal linear amplification circuit. The pulse generating circuitry and the ultrasonic return signal amplification circuitry are modular and functionally independent of each other and, consequently, may be used together in the testing system or as stand-alone instrumentation. Overall ultrasonic diagnostic system flexibility is significantly enhanced by providing improved pulser-receiver circuitry with digitally driveable computer control inputs in addition to manual controls to enable selecting initial parameters and transducer position settings. A menu-driven display machine-operator interface is also provided as a user-friendly and efficient means for setting and accessing system configuration information and test data.

Material characteristic testing method and apparatus using interferometry to detect ultrasonic signals in a web

Abstract: A non-destructive, non-contact testing apparatus and method which generally includes an ultrasonic signal generator for inducing one or more ultrasonic signals in a material and an optical interferometer that includes a laser for illuminating a section of the material and for detecting beat frequencies resulting from reflected light from the material. Deformations in the material as a result of the ultrasonic signal cause the beat frequency to be shifted as a result of the Doppler effect. Such differences in the beat frequency are detected by the system and used as an indication of a characteristic of the material.

Ultrasonic characterization of plasma-sprayed coatings

Abstract: Ultrasonic methods are developed for characterizing plasma-sprayed coatings. First, ultrasonic spectroscopy is used to determine the acoustic properties of various plasma-sprayed materials. The spectrum of overlapping back-echoes reflected on a thin plate is measured. The velocity and the attenuation coefficient of longitudinal waves are deduced from the characteristics of the spectrum at the resonant frequencies of the plate. The results show these ultrasonic properties are a good indicator to reveal differences between microstructures of coatings prepared with various plasma-spraying conditions as well as to follow their evolution after thermal treatments. Second, a pulse-echo method is developed for examining the interfaces between the components of a duplex coating through the substrate. The knowledge of the acoustic properties of the plasma sprayed materials is shown to be essential for explaining responses of coated systems. Finally, a scanning technique is used to build images of model specimens with various interface preparations.

Laser beam aiming apparatus for ultrasonic inspection

Abstract: An apparatus for aiming an ultrasonic beam to nondestructively test an object has an ultrasonic transducer for generating the ultrasonic beam having a beam axis and impinging the ultrasonic beam upon the object. The apparatus includes a laser aiming apparatus for directing at least one laser beam having a laser sight line substantially coaxial with the ultrasonic beam axis. The laser aiming apparatus, in one embodiment of the invention, includes a cross-hair apparatus for generating a laser beam cross-hair having a center along the laser sight line. Another embodiment of the present invention provides an ultrasonic mirror apparatus for bending the ultrasonic beam and which has a mirror made of a material that is substantially transparent to the laser beam. A mounting apparatus is used for initially directing a single laser beam and the ultrasonic beam along two different co-planar axes on opposite sides of the mirror and to set the mirror to bend the ultrasonic beam and align its axis with the laser beam axis so that the laser beam and ultrasonic beam axes are substantially coaxial at the object.

Process and device for the ultrasonic examination of disk elements of unknown contours shrunk onto shafts

Abstract: The invention pertains to a process and device for the ultrasonic examination of a disk element (2) shrunk onto a shaft (1) in the region of the shrink seat (3) and adjacent shrink-affected zone. The disk element (2) in cross-section has lateral faces (4, 5) which taper radially outwards from the shrink seat. The contours of the disk element (2) are scanned and thus its geometry is deduced. A geometrical reflection surface is determined. In accordance with predetermined test techniques, test parameters and positions are determined from the disk element geometry and ultrasonic test heads (9, 10) are coupled to the lateral faces (4, 5) using the test parameters thus determined to travel along the defined test paths. The associated device has a geometry recognition device which captures the geometry of the disk element (2) before the actual test. The invention facilitates time-saving examination of turbine wheel disks without the need to know their geometry beforehand.

Effects of nonlinear interaction on measurements of frequency‐dependent attenuation coefficients

Abstract: It was experimentally found that attenuation coefficient of a high‐density polyethylene sample determined by the ultrasonic spectroscopy technique strongly depends on the pressure amplitude of an incident broadband pulse applied. This result can be explained by the self‐nonlinear interaction of different frequency components of an incident broadband ultrasonic pulse (the parametric end‐fire array effect). To minimize the error due to the nonlinear effect, a guidance for choosing an appropriate pulse amplitude used in measurements based on the shock parameter was suggested.

Improving the evaluation sensitivity of an ultrasonic pulse echo technique using a neural network classifier

Abstract: In this paper, the use of an artificial neural network (ANN) for classifying weak ultrasonic signals has been attempted. The limitations of using a single conventional parameter for signal detection and classification (namely peak amplitude alone) are highlighted. Use of a multi-parameter approach is suggested. The ANN used is a multi-layered, feedforward, error-backpropagation network. Results are compared with those of conventional approaches.

Improved ultrasonic testing of railroad rail for transverse discontinuities in the rail head using higher order Rayleigh (M{sub 21}) waves

Abstract: Railroads are a very efficient and economical way of moving bulk commodities over large distances. However, like any other mode of transportation, this mode has its fair share of problems. It can be seen from the data (AAR, 1993) that over a period of time the average carload and trainload tonnage has gone up substantially. The average length of haul has also increased. However, the amount of new rail laid has actually decreased significantly. This presents a challenging opportunity to research better and more efficient ways of keeping the current railroad rail track in service and to find better ways of testing those rails to pre-empt any causes for accidents. An important factor to be considered here is the testing of the railroad rail for the amount of cold work in the top layer and the presence of microcracks in that layer. This article describes a surface guided acoustic mode with several inherent characteristics that make it particularly useful for detecting subsurface transverse flaws in railroad rail. These flaws have been previously in the blind spot of other ultrasonic NDT techniques.

Ultrasonic probe, ultrasonic probe device. process for producing piezoelectric element for use in ultrasonic probe and ultrasonic probe and ultrasonic diagnostic equipment and system using ultrasonic probe

Abstract: An ultrasonic probe comprising a coaxial cable 11 capable of transferring an energizing pulse voltage and an echo signal, at least one piezoelectric element 5, an acoustic matching layer 7 disposed on a sound transmitting face side of each piezoelectric element 5 and an acoustic backing layer 8 disposed on its opposite side, the above ultrasonic probe being adapted to transmit and receive an ultrasonic wave, wherein each piezoelectric element 5 has the following distribution of spontaneous polarization according to positions of the piezoelectric element. The spontaneous polarization of the ultrasonic probe of the present invention has differences such that the spontaneous polarization is caused to be strong at a position where the absolute value of Bessel function J0 (x/a) is large while the spontaneous polarization is weak at a position where the absolute value of J0 (x/a) is small.