Showing papers on "Ultrasonic testing published in 1993"

Surface‐breaking fatigue crack detection using laser ultrasound

Abstract: Surface‐breaking tight fatigue cracks in mild steel have been examined with laser‐generated ultrasonic pulses. Before the arrival of transmitted Rayleigh waves arriving at the detector, evidence is presented of a fast skimming longitudinal pulse which is also transmitted through the crack. Additionally, another ultrasonic feature is consistent with a longitudinal wave which is mode converted to a diffracted shear pulse by the tip of the fatigue crack. Such an interaction mechanism can form the basis of laser‐based fatigue crack depth measurements.

Apparatus for ultrasonic therapeutic treatment

Abstract: The apparatus comprises a piezoelectric vibrator (2) adapted to generate ultrasonic energy which is transmitted through an output section (4) to a plastics head (6). The shape of the head (6) may be varied to suit whichever part of a body (8) on which it is to be used. The material and shape of the head (6) is chosen to allow accurate control of frequency and amplitude of the ultrasonic energy. The preferred ultrasonic frequency is in the range of 20-120 kHz.

Flaw signature estimation in ultrasonic nondestructive evaluation using the Wiener filter with limited prior information

Abstract: Flaw signals measured in ultrasonic testing include the effects of the measurements system and are corrupted by noise The measurement system response is both bandlimited and frequency dependent within the bandwidth, resulting in measured signals which are blurred and distorted estimates of actual flaw signatures The Wiener filter can be used to estimate the flaw's scattering amplitude by removing the effect of the measurement system in the presence of noise A method is presented for implementing an optimal form of the Wiener filter that requires only estimates of the noise distribution parameters The theoretical error for scattering amplitude estimation, assuming various levels of available prior information, is analyzed Three estimation techniques, one a maximum-likelihood based method and the other two residual-sum-of-squares methods, are formulated and tested The results demonstrate that any of the three approaches could be used to optimally implement the alternative form of the Wiener filter with limited prior information >

Ultrasonic inspection system for laminated stiffeners

Abstract: An ultrasonic one pass inspection system for determining the presence, location, and size of flaws in laminated structure such as an “I” stiffener in a single inspection cycle. The exemplary system includes an immersion tank, six (6) single probes, 184 transducers, four (4) motor assemblies, two (2) encoder assemblies, a collection tank, and a recirculation assembly. The probes are designed to match the shape of the stiffener. Two (2) motors fore and two (2) motors aft of the immersion tank, produce information related to the position of the stiffener with respect to the position of the transducer. The position encoder is spring-loaded against the stiffener.

Ultrasonic reflectivity technique for the characterization of fiber‐matrix interface in metal matrix composites

Abstract: An ultrasonic plane wave reflected by a cylindrical fiber embedded in a homogeneous isotropic matrix is modeled. The model calculates the ‘‘back‐reflection’’ coefficient by taking in to account the properties of the fiber and the matrix, the ultrasonic wavelength, the angle of incidence, and a coefficient called ‘‘shear stiffness coefficient’’ which characterizes the elastic behavior between the fiber and the matrix. Results obtained from the theoretical analysis for a model metal matrix composite system are shown. The theory developed in this paper and some of the results obtained are equally applicable in ceramic matrix fiber reinforced composites.

Hybrid ultrasonic transducer

Abstract: An ultrasonic transducer employed for both transmitting ultrasonic acoustic energy into an immersion medium and for detecting acoustic energy reflected from an object under examination is provided, the transducer having a hybrid transmitter and receiver in which a ceramic piezoelectric material is used to construct a first piezoelectric element for transmitting the acoustic energy, and a polymer piezoelectric material is used to fabricate a second piezoelectric element for receiving the reflected acoustic energy. The hybrid ultrasonic transducer provides improved performance over prior transducers using only a single ceramic piezoelectric element, in that the good transmitting properties of the ceramic are preserved, while the better receiving properties of the polymer piezoelectric are used to improve the sensitivity of the transducer. The polymer piezoelectric has the further advantage of providing a closer match of acoustic impedance to the immersion fluid used in the evaluation of objects.

The use of inhomogeneous waves in the reflection–transmission problem at a plane interface between two anisotropic media

Abstract: A mathematical form is proposed for the study of the problem of reflection–transmission of monochromatic ultrasonic plane waves at the interface between two arbitrary anisotropic semi‐infinite media. The method used leads to a complete determination of all characteristics of the studied waves for all possible configurations, i.e., their directions of propagation, polarizations, and magnitudes. In particular, cases are taken into account where the waves generated by the existence of the interface are evanescent or more generally inhomogeneous. Applying this method to the calculation of several practical cases typically encountered in ultrasonic nondestructive evaluation fields, this paper points out the existence of phenomena that cannot be interpreted by classical methods usually used for the resolution of this kind of problem.

NDE of composite materials using ultrasonic oblique insonification

Abstract: The analysis of reflected ultrasonic waves induced by oblique insonification of composite materials is increasingly recognized as a powerful tool in providing information about defects and material properties. The theoretical modeling of the wave behavior for tone-burst and pulses has been very successful in accurately corroborating the experimental results. The data repeatability and accuracy make oblique insonification methods easy to standardize for practical applications. Recent theoretical and experimental results and the progress in using frequency- and time-domain data are discussed with an emphasis on the application to graphite/epoxy composites.

Absolute calibration technique for broadband ultrasonic transducers

Abstract: Calibrating an ultrasonic transducer can be performed with a reduced number of calculations and testing. A wide-band pulser is connected to an ultrasonic transducer under test to generate ultrasonic waves in a liquid. A single frequency is transmitted to the electrostatic acoustic transducer (ESAT) and the voltage change produced is monitored. Then a broadband ultrasonic pulse is generated by the ultrasonic transducer and received by the ESAT. The output of the ESAT is amplified and input to a digitized oscilloscope for Fast Fourier Transform. The resulting plot is normalized with the monitored signal from the single frequency pulse. The plot is then corrected for characteristics of the membrane and diffraction effects. The transfer function of the final plot is determined. The transfer function gives the final sensitivity of the ultrasonic transducer as a function of frequency. The advantage of the system is the speed of calibrating the transducer by a reduced number of measurements and removal of the membrane and diffraction effects.

Rapid Inspection of Composites Using Laser-Based Ultrasound

Abstract: Current techniques for automated ultrasonic inspection of airframe structures can only be used to examine limited areas which have large radii of curvature. Manual inspection techniques are required in areas having small radii. Laser-based ultrasound (LBU) offers the potential to rapidly inspect large-area composite structures having contoured geometries, without restriction to large radii of curvature [1–4]. The key components that comprise an LBU rapid inspection system are the generation and detection lasers, a 2D scanner and a suitably fast data acquisition system. These must be integrated to provide an areal scan rate of at least 100 ft2/hr based on a 0.5″ × 0.5″ pixel size. In this paper results are presented of an investigation of the relative merits of using a CO2 laser versus a Nd:YAG laser for thermo-elastic ultrasonic generation in composite materials. In our previous studies, ultrasonic C-scan images of components were acquired with the LBU system by mechanically translating the test specimen in front of the stationary generation and detection laser beams [2–4]. If the scan is to be done rapidly, this technique becomes increasingly difficult and more expensive as the mass of the part increases. To fully realize the high speed scanning potential of a same side laser-in/laser-out inspection system, it is necessary to deflect the laser beams across the part surface. An implementation of angular scanning of the generation and probe laser beams across the part surface is described. A data acquisition scheme that has been used to demonstrate data acquisition rates of 33 waveforms/sec (for 200 point waveforms) is also described.

Ultrasonic cross-correlation flowmeters

Abstract: Cross correlation transit-time measuring instrumentation can be accurate to a few parts per million depending upon the sensing technology. When ultrasonic sensors are used to measure fluid flow the accuracy is primarily determined by the fluid properties and flow profile. In multiphase mixtures, very large changes of acoustic attenuation can occur and this originally provided the impetus to produce the ultrasonic cross-correlation flowmeter. In its basic form the instrument measures the flow velocity by determining the transit time of changes of acoustic impedance, due to flow disturbances, between two parallel ultrasonic beams spaced a known distance apart. Since only the transit time is measured between two fixed marker beams, the measurement is largely unaffected by wide variations in the speed of sound in the fluid and the fluid properties. The correlation signal processor used in all trials reported in this paper was a commercially available instrument specifically designed for accurate transit time determination and velocity tracking and is based on a multichannel design system. The measurable transit time range was from 0.5 ms to 400 ms corresponding to a velocity range of 0.1 m/s to 80 m/s for a sensor spacing of 40 mm. This instrument can also process phase and amplitude modulation data simultaneously so that fluids varying from single phase to multiphase can be metered.

Direct-sequence spread-spectrum ultrasonic testing device

Abstract: Techniques for providing an ultrasonic flaw detection system are disclosed. A continuous wave of wide-band direct-sequence spread-spectrum signals continuously drives one or more transmitting transducers, thereby flooding a test object with coded ultrasound. In operation, the ultrasonic testing system is capable of reliably and predictably transmitting a high degree of ultrasonic energy (power) to a test object. Code division multiplexing correlation techniques using a variably delayed replica of a selected segment of the DSSS signal are applied to the signals received by the receiving transducers to generate a signature representing the signal returned from all reflectors within the test object.

Defect visualization in carbon fiber composite using laser ultrasound

Abstract: A non-contacting laser ultrasound system has been developed to visualize laminar defects in carbon fiber composite materials. Laser-generated ultrasound (LGU) was produced from a Nd:YAG Q-switched laser. Ultrasound was detected with the use of an actively stabilized Fabry-Perot interferometer using a 400 mW argon-ion laser source. It detected ultrasound in a typical frequency range of 1 to 10 MHz. Through-transmission C-scan measurements were made in carbon fiber composite materials of thickness 1 to 20 mm. Peak-to-peak amplitudes of the first longitudinal ultrasonic pulse were measured, with attenuation used as the basis of defect examination. Digital filtering was adopted to enhance defect visibility. Results showed that images with size resolution better than 1 mm can be achieved. Such measurements take into account any variation of surface reflectivity which can arise in industrial materials.

Laser Ultrasonic Inspection of Graphite Epoxy Laminates

Abstract: Superior mechanical properties and reduced weight of fiber reinforced polymer matrix composite laminates (e.g., made of graphite epoxy) are leading to their increased use in aeronautic and aerospace structures. These materials are found more and more in load bearing components, which in turn, requires their integrity to be fully evaluated by nondestructive inspection. This applies to newly manufactured parts which can be flawed following improper manufacturing procedures and to parts which have been in service on an aircraft as well, since additional flaws could have occurred and old existing flaws could have grown and become more severe. Flaws which are found in these materials include porosity and foreign inclusions, which are produced during manufacturing and delaminations between plies, which can be produced at manufacturing or can be caused by the impact of foreign objects on the structure. Ultrasonics has been recognized to be a superior technique for detecting delaminations and can be used to detect foreign inclusions and assess porosity, as well [1,2]. The ultrasonic waves are usually generated and detected by piezoelectric transducers and coupled to the inspected part by direct contact or water. Although operation in transmission is widely used and easily implemented for curved parts, the pulse-echo mode is preferred since it requires only single side access and provides flaw depth information. In this case, the transducer should be properly aligned with respect to the surface of the inspected part (within a few degrees), since it is a phase sensitive device emitting and its whole surface.

On the influence of frequency and width of an ultrasonic bounded beam in the investigation of materials: Study in terms of heterogeneous plane waves

Abstract: Theoretically obtained three‐dimensional plots showing the behavior of the reflection coefficient for heterogeneous plane waves upon arbitrary layered media as function of incidence angle and heterogeneity, supply valuable information for the investigation of the reflector when using bounded ultrasonic beams. The presence of leaky interface modes and their angular positions for a specific sample are determined by the fd products (frequency times thickness) of the constituent layers. Deformations of the reflected and transmitted bounded beam profiles and the contribution of surface wave radiation (leaking energy) at vibrational mode angles are governed by the fW product (frequency times beamwidth). For a given layered medium, optimum conditions for observing particular mode vibrations and large deformations of reflected ultrasonic profiles can be predicted theoretically.

Laser ultrasonic inspection of honeycomb aircraft structures

Abstract: Ultrasonic methods have been used extensively for the inspection of advanced composite materials and adhesively bonded structures. Conventional ultrasonic inspections usually require couplants to propagate ultrasonic waves to and from the part surface. Delaminations, porosities, and foreign inclusions in composite laminates can be successfully detected by pulsed-echo and through-transmission modes of ultrasonic inspection. Debonds in adhesively bonded structures are most effectively detected by the through-transmission mode of ultrasonic inspection.

Using ultrasonics for sensing in a robotic environment

Abstract: A system based on pulsed ultrasonics is developed to be applied for sensor feedback in robotics. A sensor device consisting of four 40-kHz transducers mounted around one 200-kHz transducer is designed. By changing the frequency between 40 and 200 kHz for the ultrasonic excitation, the range of the distance measurements is significantly increased while the accuracy is maintained. The system can perform distance measurements as well as space orientation and object identification among a limited number of possible forms. Particular algorithms are developed to detect the front of the reflected echo of the ultrasonic transducers. A special computer interface has been designed for fast sampling of the ultrasonic signals. The system is built around a laboratory robot platform. Experimental results of both object identification and sensor based feedback are described. >

Novel Stage for Ultrasonic Measurement of Real Contact Area Between Rough and Flat Parts Under Quasi-Static Load

Abstract: The paper contains a description of an ultrasonic method and stage for real contact area (RCA) measurement on steel flat parts with technological surface layer The stage allows measurement of RCA of test surface in contact with a rigid flat counterface The measurement can be taken during the process of surface deformation as well as for the surfaces already deformed

An intelligent ultrasonic inspection system for flooded member detection in offshore structures

Abstract: An ultrasonic system for automatic underwater inspection of steel jacket offshore installation is described. It is based on the unambiguous detection of water ingress in normally sealed tubular members, thereby providing an indication of through-wall structural failure. A novel transducer design, based on a dual frequency array of 1-3 connectivity thickness drive transducers, is used to provide the required sensitivity and act also as an environmental monitor for input to an expert system, which performs automatic data analysis. Although intended primarily for operation on a remotely operated vehicle, the system may be employed satisfactorily by a driver. A series of test trials is described, and the prototype is shown to perform very well for all intended modes of operation. >

Method and apparatus for ultrasonic inspection of inaccessible areas

Abstract: A method and apparatus which uses ultrasonic techniques to inspect critical pipe joints and other critical industrial areas that are normally inaccessible. A waveguide (20, 46) including one or more flexible fibers (72) is embedded in concrete (12) or whatever else embeds the piping which includes the critical area. One end of the waveguide (20, 46) is accessible so that an ultrasonic transducer (30) can be used to transmit ultrasonic signals along the waveguide (20, 46) and receive reflected echoes to provide an ultrasonic image of the critical area. In a case where the area to be inspected is submerged, the waveguide (20, 46) takes the form of a flexible fiber bundle which is manipulated until its end is adjacent to the critical area. Some of the fibers (72) in the bundle can be used to illuminate the critical area, and other fibers (72) can transmit optical images for display on a video monitor (78).

Acoustic and Ultrasonic Signals as Diagnostic Tools for Check Valves

Abstract: A typical nuclear plant has between 60 and 115 safety-related check valves ranging from 2 to 30 in. The majority of these valves control water flow. Recent studies done by the Institute of Nuclear Power Operations (INPO), Electric Power Research Institute (EPRI) and the US Nuclear Regulatory Commission (NRC) found that many of these safety-related valves were not functioning properly. Typical problems found in these valves included disk flutter, backstop tapping, flow leakage, disk pin and hinge pin wear, or even missing disks. These findings led to INPO's Significant Operating Experience Report (SOER, 1986), and finally, NRC generic letter 8904, which requires that all safety-related check valves in a nuclear plant be regularly monitored. In response to this need, the industry has developed various diagnostic equipment to monitor and test check valves, using technologies ranging from acoustics and ultrasonics to magnetic - even radiography has been considered. Of these, systems that depend on a combination of acoustic and ultrasonic techniques are among the most promising for two reasons: these two technologies supplement each other, making diagnosis of the check valves much more certain than any single technology, and this approach can be made nonintrusive. The nonintrusive feature allows the checkmore » valves to be monitored and diagnosed without being disassembled or removed from the piping system. This paper shows that by carefully studying the acoustic and ultrasonic signatures acquired from a check value, either individually or in combination, an individual with the proper training and experience in acoustic and ultrasonic signature analyses can deduce the structural integrity of the check valve with good confidence. Most of the conclusions are derived from controlled experiments in the laboratory where the diagnosis can be verified. Other conclusions were based on test data obtained in the field.« less

Transient elastic wave generation by an array of thermoelastic sources

Abstract: A set of 16 thermoelastic strip sources, equivalent to a phased array of ultrasonic transducers has been implemented on a solid by irradiating its surface with a multiple beam pulsed YAG laser. Longitudinal elastic waves were focused in the sample by time delaying each laser pulse. Results of experiments performed on duraluminum in the thermoelastic regime are presented and compared with simulations based on the surface center of the expansion model. It is shown that with this technique, a high energy focusing, together with an ultrasonic beam scanning can be achieved in a wide angular range leading to a significant improvement in the signal‐to‐noise ratio of a laser based ultrasonic system.

Calibration and flaw detection method for ultrasonic inspection of acoustically noisy materials

Abstract: A method and apparatus for the ultrasonic inspection of acoustically "noisy" specimens, such as those having intrinsically coarse grain structure (e.g., turbine rotor parts made of superalloy compositions) employs several types of ultrasonic diagnostic measurement techniques, including at least: "Pitch-Catch" analysis and "Pulse-Echo Axial Long-Wave" analysis. When a Pitch-Catch technique is utilized, a "through-transmitted" sound wave is acquired for each specimen tested and used as a calibration standard to normalize ultrasonic inspection test data for that specimen prior to any automated defect/flaw detection and sizing processing. The through transmitted sound wave is also used to equate the amplitude of "indications" (i.e., significant detected ultrasonic reflections) to that of a standardized theoretical reflector of known size (e.g., an equivalent "flat bottom hole" or EFBH reflector) so that the test sensitivity or "size of indications" can be uniquely determined for each specimen on which the test is performed. When a Pulse-Echo technique is utilized, a through-transmitted sound wave is not used (since this technique employs only a single transducer) and inspection data is instead normalized by a "back wall" reflection signal. Once ultrasonic inspection test data is obtained and digitized, a "rolling average" of the data is used to estimate the localized noise level within the material under test. For every transducer pulse data point obtained, a unique signal-to-noise (S/N) ratio is computed. Variations in S/N ratio for the material are measured at each axial slice of material volume inspected. A function of the standard deviation of the S/N values is then used to automatically adjust a detection amplitude threshold to optimize the flaw detection process and minimize false alarms.

Advanced Ultrasonic Probes for Scanning of Large Structures

Abstract: Rapid and quantitative ultrasonic testing of large composite or bonded structures can be achieved using scanning ultrasonic probes Liquid-jet probes, air coupling transducers and laser stress wave sensors enable non-immersion ultrasonic measurements The ability of these scanning ultrasonic probes to retain the true acoustical waveform is critical for scan signal analysis and reproducibility of measurements With advancement of high-speed digitizing instrumentation, the overall ultrasonic test-scan data are often limited by fidelity of sensors In addition, the combination of different probes such as low-noise ultrasonic liquid jet probes and non-contact laser stress wave sensors significantly improves reproducibility of coupling, retention of signalwaveform and flexibility in ultrasonic test geometry Quantitative evaluation of scanning probes, such as stand-off signal to noise and frequency bandwidth, define realistic performance of such probes

Apparatus and method for ultrasonic reconstruction and testing of a turbine rotor blade attachment structure

Abstract: An apparatus and method for ultrasonic reconstruction and testing of a non-visible turbine rotor blade attachment structure is described The method of the invention includes positioning transducers at a first location to obtain slot region scan data corresponding to a slot region of the non-visible turbine rotor blade attachment structure, and positioning transducers at a second location to obtain straddle-mount region scan data corresponding to a straddle-mount region of the non-visible turbine rotor blade attachment structure The shape of the non-visible turbine rotor blade attachment structure is reconstructed from the slot region scan data and the straddle-mount region scan data to form reconstruction data The reconstruction data is used to select test scan positions for ultrasonic testing Ultrasonic testing is then performed at the selected test scan positions

A 5 MHz high-voltage demultiplexed ultrasonic array system for rapid-scan testing of advanced materials

Abstract: The most common techniques in non-destructive ultrasonic testing applications make use of the mechanical or manual scanning of the sensor devices. An important limitation of these procedures is the time required to acquire the inspection data when only a single transducer is scanned over the whole area of interest. To overcome this problem, a multichannel operation must be introduced. In this paper a 5 MHz array system of eight channels with electronic scanning through a high-voltage demultiplexer is presented. The system has been specially developed for rapid-scan purposes, needing only one commercial monochannel flaw detector as external equipment. The sensor device is a broad-band eight-element array transducer of multilayer type with one matching layer. A new analog demultiplexer has been designed, which is able to control the pass of broad-band pulses containing large peaks of voltage and current.

Time-Domain Ultrasonic NDE of the Wave Velocity of a Sub-Half-Wavelength Elastic Layer

Abstract: The purpose of this paper is to report a new technique for ultrasonic NDE of the wavespeed of a sub-half-wavelength layer (given its thickness) using only the time-domain information. The new technique was applied to aluminum plates with h λ ranging from 0.082 to 2.0 where h and λ are the plate thickness and the nominal wavelength, respectively. A satisfactory compatison between the measured values and the nominal value was observed.

Method of suppressing grain noise in ultrasonic waveform data by 3D filtering

Abstract: A method of suppressing grain noise resulting from ultrasonic inspection of an object, including ultrasonically scanning an object and detecting waveform signals therefrom, determining, from the signals, data values which define a 3D waveform data set U(x,y,t) having both spatial (x,y) and temporal (t) ultrasonic data values from the scanned object, converting the 3D waveform data set into a 3D filtered waveform data set V(x,y,t) by performing a 3D filtering operation thereon, wherein for each data value in the 3D waveform data set U(x,y,t), a filtered data value is obtained by taking into account data values which are adjacent thereto both spatially and temporally, thereby reducing grain noise relative to flaw signals to enable a high probability of flaw detection and a low probability of false flaw indications.