Showing papers on "Ultrasonic testing published in 1992"

Double through‐transmission bulk wave method for ultrasonic phase velocity measurement and determination of elastic constants of composite materials

Abstract: This paper describes a modification of a nondestructive ultrasonic method for measurements of the phase velocity of bulk waves in arbitrary directions in generally anisotropic materials. In the conventional method the through‐transmission technique is used for velocity measurements at a specified angle of incidence. When this angle is changed by rotation of the sample, the transmitted beam changes position, and so the position of the receiving transducer must be changed. This leads to experimental difficulties and loss of precision. In the double‐transmission technique, the ultrasonic wave is reflected from reflector plates behind the sample and returns via the same path to the same position on the transmitter/receiver working in pulse‐echo mode, which eliminates the necessity of readjusting the receiver position. It is also shown that for arbitrary direction of measurement in anisotropic materials, time‐delay measurements give phase velocity regardless of the angle of deviation between phase and group ve...

Simultaneous ultrasonic velocity and sample thickness measurement and application in composites

Abstract: Ultrasonic velocity is widely used in the investigation of material properties. In cases where thickness of the test piece is not precisely known or varies spatially, it is desirable to determine the wave velocity and the sample thickness in the same ultrasonic measurements. For tests in an immersion tank or using squirters, both wave velocity and the specimen thickness may be deduced from the time of flight of several ultrasonic pulses. In this paper four different configurations of pulse echo and through transmission are described for the ‘‘simultaneous’’ velocity and thickness determination. The method is then applied to investigate the porosity content in graphite/polyimide and graphite/epoxy composite laminates. Good results were obtained for both the wave velocity and the part thickness, and a clear correlation between velocity and void content is demonstrated.

Nondestructive evaluation of ferromagnetic cables and ropes using magnetostrictively induced acoustic/ultrasonic waves and magnetostrictively detected acoustic emissions

Abstract: A method and apparatus for the nondestructive evaluation of ferromagnetic and non-ferromagnetic materials, particularly wire ropes, cables, and strands, and pipes utilizing the magnetostrictive effect for measuring minute variations in magnetic fields and characterizing these minute variations as indicative of the acoustic/ultrasonic behavior of fractures, cracks, and other anomalies within a substance under evaluation. The apparatus and method contemplate both an active testing application, wherein a transmitting sensor generates an acoustic/ultrasonic pulse within a material through the magnetostrictive effect and a second receiving sensor detects reflected acoustic/ultrasonic waves within the material, again by the inverse magnetostrictive effect. The advantages of utilizing magnetostrictive sensors as opposed to well known piezoelectric sensors lies in the ability to generate and detect acoustic/ultrasonic waves without a direct physical or acoustical contact to the material. The apparatus and method of the present invention also anticipates the use of a passive monitoring system comprised only of a receiving magnetostrictive sensor that continuously monitors a ferromagnetic or non-ferromagnetic substance for acoustic emissions and either records this monitored information or alerts the appropriate personnel of the existence of an acoustic emission indicating deterioration within the structure.

The propagation and attenuation of medium-frequency ultrasonic waves in concrete: a signal analytical approach

Abstract: The manner in which medium-frequency ultrasonic pulses travelling through concrete are generated, received, digitized and analysed is described Due to the highly attenuating nature of this medium and its differential effects on the frequency composition of broad-band signals, signal analysis was performed by partitioning the signal into discrete windows in the time domain, corresponding to the emergence of individual wave phenomena within the medium These windows were then transformed to the frequency domain for subsequent filtering and interpretation Experimentation combined with theoretical modelling has shown that the appearance and decay of discrete frequency bands depends on both the composition of the concrete, termed the resonance phase, and its external importance with respect to the ultrasonic inspection of concrete and other such inhomogeneous materials

Method of simulating ultrasonic inspection of flaws

Abstract: A method for simulating in real-time the ultrasonic inspection of flaws in power plant components such as piping stores the X, Y and skew data relating to a specific waveform and a specific flaw in a unique format in a multi-disk rotational data storage. The skew angles are respectively stored on one side of a disk with the X-axis data relating to tracks on the disk and the Y-axis data to sectors on the disk. In this manner waveform data of several bytes which represent a defect or flaw can be retrieved and displayed to the user of this simulation system. A RAM is utilized as a cache memory.

An iterative ray tracing model for ultrasonic nondestructive testing

Abstract: This paper describes a three-dimensional ray tracing model for predicting ultrasonic energy propagation in anisotropic and inhomogeneous materials. The model has recently been developed to be an iterative tool, capable of calculating energy paths between specified start and end points. This two-point ray tracing is presented and its value for predicting energy paths between transducers and postulated defects is discussed. Applications of the model to problems of interest to ultrasonic nondestructive testing are presented. These include assessment of inspection methods for austenitic components, such as cladding and welds. In particular, defect location and sizing errors are calculated for underclad defects at a variety of depths below a layer of cladding, and for backwall breaking defects in and around a single V-weld. For the calculations considered, we find these errors generally to be small, except for defects close to the cladding layer, where significant underestimation of the distance between the top of the defect and the cladding occurs.

Titanium article having improved response to ultrasonic inspection, and method therefor

Abstract: A titanium alloy billet having improved response to ultrasonic inspection is described. The billet is given a thermomechanical treatment above the beta transus of the alloy immediately prior to ultrasonic inspection. The treatment may include beta annealing or mechanical deformation above the beta transus. The invention is particularly effective for beta-stabilized alpha-beta and beta titanium alloys.

A high precision ultrasonic system for vibration measurements

Abstract: A microcomputer‐aided ultrasonic system that can be used to measure the vibratory displacements of an object is presented. A pair of low cost 40‐kHz ultrasonic transducers is used to transmit ultrasound toward an object and receive the ultrasound reflected from the object. The relative motion of the object modulates the phase angle difference between the transmitted and received ultrasound signals. A single‐chip microcomputer‐based phase detector was designed to record and analyze the phase shift information which is then sent to a PC‐AT microcomputer for processing. We have developed an ingenious method to reconstruct the relative motion of an object from the acquired data of the phase difference changes. A digital plotter based experiment was also designed for testing the performance of the whole system. The measured accuracy of the system in the reported experiments is within ±0.4 mm and the theoretical maximal measurable speed of the object is 89.6 cm/s. The main advantages of this ultrasonic vibratio...

Absolute ultrasonic displacement amplitude measurements with a submersible electrostatic acoustic transducer

Abstract: An experimental technique for absolute measurement of ultrasonic wave particle displacement amplitudes in liquids is reported. The technique is capable of measurements over a frequency range of two decades with a sensitivity less than one angstrom. The technique utilizes a previously reported submersible electrostatic acoustic transducer (ESAT) featuring a conductive membrane stretched over a recessed electrode. An uncertainty analysis shows that the displacement amplitude of an ultrasonic plane wave incident on the ESAT can be experimentally determined to better than 2.3-4 percent, depending on frequency, in the frequency range of 0.5-15 MHz. Membranes with lower and more uniform areal densities can improve the accuracy and extend the operation to higher frequencies.

Power‐law relationships between the dependence of ultrasonic attenuation on wavelength and the grain size distribution

Abstract: Grain size is one of the factors that influence mechanical properties of metals like strength and fracture toughness. Ultrasonic waves propagating in polycrystalline materials are subject to attenuation dominated by grain boundary scattering. The importance of grain size estimation for industrial applications warrants the investigation of alternative methods of nondestructive grain size determination. Analysis of the power‐law behavior of ultrasonic attenuation experimental data is used to link the wavelength dependence of the attenuation coefficient directly to the grain size distribution. The outcome is a simple relationship between the power law that describes the grain size distribution and the power‐law dependence of attenuation on wavelength. Careful attention is given to the limitations in terms of a practical grain size distribution with finite limits. Two types of measurements are presented to verify the theoretical development: grain size distribution and ultrasonic attenuation. Nickel samples w...

Pulse-echo and through transmission lamb wave techniques for adhesive bond inspection

Abstract: The possibility of increasing the sensitivity and efficiency of adhesive bond inspection by utilizing ultrasonic Lamb waves in a contact mode is demonstrated. Both Pulse-Echo and Through Transmission type transducer arrangements are considered. The basic theory behind both techniques is addressed and experiments are performed on several different specimens of aluminium-to-aluminium adhesively bonded lap joint structures containing programmed debond simulations. It is shown that, if the proper ultrasonic inspection parameters such as transducer frequency and incident angle are chosen to efficiently generate a specific lamb wave mode, a map of the amplitude of the transmitted or reflected Lamb wave can serve to locate the debond regions within the bondline

Resonant electromagnetic excitation and detection of ultrasonic waves in thin sheets

Abstract: A unified theory of the simultaneous electromagnetic excitation and detection of ultrasonic waves travelling in the through‐thickness direction in conducting sheets in the presence of a static magnetic field is presented. What to our knowledge are the highest‐frequency room‐temperature measurements of this type are described for aluminium sheets of thickness as low as 20 μm for frequencies up to 120 MHz. Maxwell’s equations are solved for the geometry of a planar current sheet above a conducting sheet with sinusoidal time variation. It is shown how, from the solution of a single fourth‐order differential equation for the magnetic vector potential, the coupled electromagnetic and elastic wave problem can be solved analytically. The effective transfer impedance is evaluated, a measure of the ultimate efficiency of the combined excitation and detection process. At acoustic resonance its amplitude is inversely proportional to the sum of the ultrasonic attenuation of the sample and the attenuation arising from...

Ultrasonic fluid flow measurement method and apparatus

Abstract: An apparatus for measuring the flow of a fluid in a pipe using ultrasonic waves. The apparatus comprises an ultrasonic generator, a lens for focusing the sound energy produced by the generator, and means for directing the focused energy into the side of the pipe through an opening and in a direction close to parallel to the long axis of the pipe. A cone carries the sound energy to the lens from the generator. Depending on the choice of materials, there may be a quarter-wave, acoustic impedance matching section between the generator and the cone to reduce the reflections of energy at the cone boundary. The lens material has an acoustic impedance similar to that of the cone material but a different sonic velocity so that the lens can converge the sound waves in the fluid. A transition section between the lens and the fluid helps to couple the energy to the fluid and assures it is directed as close to parallel to the fluid flow direction as possible.

Method of ultrasonic inspection of materials through opaque barriers

Abstract: An improved apparatus and method for ultrasonic inspection of materials through barriers such as gaps in manufactured parts is disclosed. The improvement herein is directed to enabling such ultrasonic testing to bridge ambient gaps such as intentionally formed gaps in composite structures having a first structure for originally receiving and transmitting sound separated by the gap from another structure to be inspected. Preferably, the gap is flooded with a gas having a predictable and optimum speed of sound relative to the material of the first and second structures. Sound is propagated to the first structure in a wave packet that is transmitted through the couplant fluid. The sound is generated in a wave packet having a spatial width at least twice the dimension of the gap to be bridged. The wave packet has a contained frequency having a wavelength (relative to the speed of sound of the gas flooding the gap) to create a constructively interfering standing wave node within the gap. The sound propagated to the gas-filled gap has a wavelength which is a half-integer with respect to the gap dimension. Sound passes through the first structure, creates a standing wave node in the gas-filled gap, passes into and acoustically interrogates the second structure for flaws and reflects. Reflected ultrasoound from the interrogated second structure again bridges the gap as a constructively interfering standing wave, passing through the primary structure and then through the couplant fluid to a transducer for receipt and analysis of the received ultrasound.

Fluid density and concentration measurement using noninvasive in situ ultrasonic resonance interferometry

Abstract: A method of noninvasively measuring the density of fluids contained within pipes, cans, tanks, and bottles has been developed. The container-fluid system is interrogated using an ultrasonic transducer. A second transducer is used to observe transmitted energy as the input frequency is swept through an appropriate range determined by the geometry. Resonance peaks are observed in the transmitted energy. The periodicity of the resonant peaks is determined by analyzing the response data using a fast Fourier transform. The technique is tested using known NaCl concentration standards within a stainless steel pipe. The concentration of unknown NaCl solutions is measured in situ with an accuracy of +or-0.15 M over a range of 0.4 to 3.4 M corresponding to an accuracy of +or-0.02 specific gravity (SG) units over a range of 1.000 to 1.134 SG units. >

A Critique of the Ultrasonic Pulse Velocity Method for Testing Concrete

Abstract: The pulse velocity method is the most widely used ultrasonic nondestructive method for assessing concrete quality. However, it has been well established that the relation between ultrasonic pulse velocity and concrete strength is, in general, not reliable enough for practical purposes; nevertheless, essentially the same method has been used for over 40 years. This paper is a critical analysis of the existing ultrasonic pulse velocity method as well as an attempt to explain it's failure for strength determination and damage detection in concrete. First, the theory and technique of the ultrasonic pulse velocity method is introduced. Next, misconceptions concerning the relation between pulse propagation parameters and concrete strength are clarified. In addition, original experimental data are presented that demonstrate the insensitivity of the ultrasonic pulse velocity method to the present strength of a variety of materials including concretes, mortars, and pastes. The end result of this study is a better understanding the ultrasonic pulse velocity method - as applied to concrete - as well as a better understanding of the limitations of this technique.

Ultrasonic scattering by a flat-bottom hole in immersion testing: An analytical model

Abstract: In ultrasonic nondestructive evaluation tests, a flat‐bottom hole is often used as a reference scatterer for calibration, sensitivity, and sizing studies. Here, an analytical model is derived for the response of a flat‐bottom hole in an immersion testing setup where the model is not restricted to the small hole, far‐field conditions required by previous theories. Tests of the model demonstrate that it is able to predict single frequency DGS curves for the hole that agree well with experiments, even in the very near field of the transducer. Thus, the model may serve as a new and useful theoretically based calibration ‘‘standard’’ for a variety of ultrasonic applications.

Calibration block and method for an ultrasonic system

Abstract: An ultrasonic calibration block for standardizing an output of a pulse-echo ultrasonic inspection system is provided with an insonification surface for receiving ultrasonic pulses from the inspection system and a plurality of reflective interfaces stacked on top of one another and positioned at different distances from the insonification surface, each reflective interface having a different and characteristic reflectivity. A method of calibrating the output of the inspection system, using the calibration block, employs standard waveforms generated by insonifying the calibration block to generate a look-up table of standard waveform amplitudes related to a standardized output of the inspection system for a given material of a part to be inspected.

Tenon inspection systems and methods

Abstract: An ultrasonic inspection system uses a submerged ultrasonic transducer to provide an ultrasonic beam focused to a small spot on a submerged surface of a member to be internally inspected. By use of a focused beam projected through a fluid, such as water, to a submerged surface, the ultrasonic energy is efficiently coupled to a surface area which may be small and/or of irregular or curved shape. Systems and methods for inspecting turbine rotor blade tenons permit a turbine rotor with hundreds of blades to be rotated past a submerged transducer with automatic recording and processing of ultrasonic echoes to develop two-dimensional color images of internal portions of tenons at which cracks may typically occur. Automated adjustment of beam focusing of a transducer including an array of elements and threshold monitoring of fault-indicative echo returns are provided for.

Ultrasonic C-Scan Inspection Of Composite Materials

Abstract: Ultrasonic technique using an automated C-scan has been established as the primary inspection method for composite materials. In this paper, the principles of ultrasonic inspection, the type of defects that may be generated during fabrication and/or during service of fibre-reinforced composites and their detection using ultrasonic techniques are described. Emphasis is placed on the capabilities and limitations of ultrasonic techniques in testing composites. The material used in the present study was graphite/epoxy.

Ultrasonic inspection method for detecting defects in solid objects

Abstract: A non-destructive, non-invasive arrangement is provided for detecting defects, such as voids, or poorly adhering layers in solid objects and laminated materials. A sensing signal is emitted by one transducer and received by two others. All of the sensors are disposed in a housing unit. The difference between the received signals is used to indicate a defect in the work piece proximate one of the transducers.

Ultrasonic inspection of very thin adhesive layers

Abstract: It is shown here that ultrasonic measurements can provide accurate information on an adhesive layer whose thickness is negligible compared with the wavelength. In this case, the adhesive layer can be considered as a simple interface between two elastic solids. This kind of contact enables small discontinuities of stresses or displacements between both substrates. A simple formulation is introduced to take into account these discontinuities expressed in terms of imperfect boundary conditions. It is shown that this formulation is consistent with exact calculation in layered media. The range of applications of this model and its limits is also investigated. This model is used to infer quantitative data on the changes in mechanical properties of a thin bonding layer (about 5 μm) from reflection coefficient measurements during its hardening process. The results obtained are in excellent agreement with ultrasonic measurement in bulk.

Ultrasonic testing apparatus

Abstract: PURPOSE:To enable the scanning of an ultrasonic transmitter/receiver by a linear scanning or a radial scanning by a method wherein an ultrasonic probe is made connectable to a linear operation unit while a radial operation unit is connected to the linear operation unit and the ultrasonic probe is connected to the radial operation unit. CONSTITUTION:An ultrasonic probe 1 is made connectable to either a linear unit 10 or a radial operation unit 50. The linear operation unit 10 is operated to push or pull an inserting member 2 so that a linear scanning of an ultrasonic transmi-tter/receiver 4 is performed over a specified range. The linear operation unit 10 is provided with a cord 20 for ultrasonic waves to give and take ultrasonic signals between the ultrasonic transmitter/receiver 4 and an ultrasonic observer T. The radial operation unit 50 is connected to the linear operation unit 10 to allow the mounting of the ultrasonic probe 1. A signal transmission means is mounted in a body casing 50a to transmit ultrasonic signals transmitted or received between the ultrasonic transmitter/receiver 4 and the linear operation unit 10.

Method and system of measuring ultrasonic signals in the plane of a moving web

Abstract: An improved system for measuring the velocity of ultrasonic signals within the plane of moving web-like materials, such as paper, paperboard and the like. In addition to velocity measurements of ultrasonic signals in the plane of the web in the machine direction, MD, and a cross direction, CD, generally perpendicular to the direction of the traveling web, therefor, one embodiment of the system in accordance with the present invention is also adapted to provide on-line indication of the polar specific stiffness of the moving web. In another embodiment of the invention, the velocity of ultrasonic signals in the plane of the web are measured by way of a plurality of ultrasonic transducers carried by synchronously driven wheels or cylinders, thus eliminating undue transducer wear due to any speed differences between the transducers and the web. In order to provide relatively constant contact force between the transducers and the webs, the transducers are mounted in a sensor housings which include a spring for biasing the transducer radially outwardly. The sensor housings are adapted to be easily and conveniently mounted to the carrier to provide a relatively constant contact force between the transducers and the moving web.

Performance evaluation of frequency diverse Bayesian ultrasonic flaw detection

Abstract: The performance of an ultrasonic flaw detection system is valued by the success of differentiating the flaw echoes from those echoes scattered by microstructures (e.g., grains in polycrystalline metals). Microstructure noise (clutter) is stationary and will only vary when the frequency of the ultrasonic beam is changed. In this paper, frequency diverse microstructure information is obtained through the split‐spectrum processing of broadband ultrasonic backscattered echoes. The statistical difference between clutter and flaw echoes over different frequency bands has led to the development of a Bayes classifier that is quadratic and can incorporate the correlation properties of scattered echoes. The performance of the Bayes classifier has been examined for both experimental and computer simulated data, and compared to other commonly used techniques such as mean, minimum, median, and polarity detectors. The Bayes classifier shows superior performance, and the flaw‐to‐clutter visibility has been improved in t...

New developments in piezoelectric polymer ultrasound transducers and transducer systems

Abstract: Piezoelectric polymers, such as PVDF and its copolymers, are finding increased use for ultrasound transducers in both medical and nondestructive testing applications. Because of their inherent properties of high compliance, low acoustic impedance, availability in large areas, and broadband acoustic performance, they are particularly useful in medical applications that require miniature transducers for high-frequency/high-resolution and low ultrasonic penetration, such as invasive medical imaging. The technology also provides great utility in nondestructive testing applications which require low-profile ultrasonic inspection of fiber-composite structures, especially for non-planar surfaces. This paper reviews some recent developments in piezoelectric polymer ultrasound transducer technology in both the medical and nondestructive testing (NDT) application areas. The presentation covers recent developments in invasive medical ultrasound transducers and transducer systems that employ the piezoelectric polymer technology for such applications as intraluminal imaging of the coronary arteries. A discussion of piezoelectric polymer ultrasound sensor arrays for NDT of fiber composite structures is also included.

The thermoelastic surface strip source for laser‐generated ultrasound

Abstract: The vertical ultrasonic surface displacement generated by a laser‐induced, thermoelelastic, rectangular surface strip source is formulated. The main features of this source, ultrasonic rise times comparable to those of the generating light pulse derivatives, and a large amplitude, double‐pulsed waveform, are advantageous for ultrasonic spectral‐ and time‐domain measurements for nondestructive material evaluation. The analysis shows that, for laterally symmetric sources in the thermoelastic regime, only one tangential thermoelastic stress component contributes to the vertical displacement. Therefore, the strip source is equivalent to two, tangential line forces acting outward at the strip’s front and back edges. The leading‐edge rise time of the signal is virtually independent of the lateral extent of the source, which mostly affects the trailing portions of the ultrasonic pulses. Consequently, a particularly simple expression, which compares favorably with experimental results, is obtained for short strip...