S. A. Titov

Pulse-echo NDT of adhesively bonded joints in automotive assemblies.

A new method for the detection of void-disbonds at the interfaces of adhesively bonded joins is considered. Based on a simple plane wave model, the output waveform is presented as a sum of two responses associated with the reflection of the ultrasonic wave at the first metal-adhesive interface and the second metal-adhesive interface, respectively. The strong response produced by the wave reverberating in the first metal sheet is eliminated through comparison between the pulse-echo signal measured at the area under the test and reference waveform recorded for the bare first metal sheet outside of the joint. The developed decomposition algorithm has been applied to the study of steel and aluminum samples having various adhesive layer thicknesses in a range of 0.1-1mm.

Wide-aperture, line-focused ultrasonic material characterization system based on lateral scanning

We present a new wide-aperture, line-focused ultrasonic material characterization system. The foci of the transmitting and receiving transducers are located in the specimen-immersion liquid interface; and the output voltage V(x, t) of the system is recorded as a function of the lateral position of the receiving transducer. The two-dimensional spectrum of V(x, t) can be expressed as a product of the transfer function of the system and the reflectance function of the interface. In comparison with a system based on scanning in the z direction, the angular resolution of the proposed technique increases with decreasing angle of incidence. There are no geometrical restrictions on the length of the recorded spatial data and the angle of incidence in the case of lateral scanning. The temperature coefficient of the measurement error is low because of the constancy of the propagation distance of ultrasound in the immersion fluid during data acquisition.

V(x,t) acoustic microscopy method for leaky surface acoustic waves parameters measurements

In this paper, a new method for the measurement of the acoustical parameters of the laterally uniform specimen is considered. Two focused large angular aperture transducers are used in this technique. Foci of the transducers are placed on the specimen surface and received voltage V(x,t) is acquired during the relative transducers translation along the specimen surface. Due to geometry of the ultrasonic system, angular range of the generated and detected waves can be close to (0, /spl pi//2) and the length of the recording distance is unlimited. Velocity and attenuation of the leaky wave measured by this method do not depend on the temperature of the immersion liquid. Also, contrary to V(z) method, angular resolution of the V(x,t) method is better for small incident angles.

4I-2 Ultrasonic Pulse-Echo NDE of Adhesive Bonds in Sheet-Metal Assemblies

The development of a 20 MHz pulse-echo method for nondestructive evaluation (NDE) of adhesive bonds was undertaken to provide assurance of bond integrity in vehicle body assemblies. This new NDE method features improvements over previous methods implemented in production, and extends the range of bond evaluation effectiveness. The NDE is accomplished by the acquisition and analysis of acoustic echoes that return from bond joints that have interfaces between layers with large acoustical impedance mismatch. These echoes reverberate in the multilayered joint structures and are captured for a computer-automated analysis that provides a rapid interpretation of the indications, and subsequently yields a simplified display of the inspection results

Doppler continuous wave scanning acoustic microscope

A modification of V(z) method is presented in this paper. It is proposed to use the Doppler effect in the continuous wave reflection scanning acoustic microscope. The Doppler frequency shift is created due to constant velocity movement of the lens perpendicular to the sample surface. A Doppler continuous wave microscope with an operating frequency of 300 MHz was developed. The device was tested on the investigations of the materials with known acoustical parameters.

Evaluation of the V(x) temperature stability in time-resolved ultrasonic measurements

Thermal errors of time-resolved ultrasonic material characterization systems are considered. For V(z) data acquisition configuration, theoretically estimated the thermal error coefficient of leaky wave velocity was found to be 10/sup -3/ 1//spl deg/C. It was shown that the reading of the sound velocity in immersion liquid is not required for V(x) data processing. The thermal error coefficient estimated experimentally in 20-50/spl deg/C range with the developed V(x) system is 5/spl middot/10/sup -5/ 1//spl deg/C for a water-fused quartz interface.

An ultrasonic array technique for velocity of bulk waves and sample thickness measurement

The ultrasonic array technique for simultaneous measurement of the bulk wave velocity and thickness of a plate sample is proposed. In the proposed methods, the elements of the array send waves toward the specimen and receive echoes reflected from the front and back surfaces of the sample. The full array data set is used for calculation of the responses of the longitudinal and shear plane waves in the “angle of incidence — time” space. The unknown parameters of the specimen can be estimated by fitting the theoretical model for the time delays of these responses to the experimental data. The 32-element linear array, having a central frequency of 15 MHz, was used in the experiment. It was found that the relative errors of the velocity and thickness measurements are in a range of 1–2%.

3B-5 Development of an Ultrasonic Array Technique for LSAW Measurement

An ultrasonic method of leaky surface acoustic waves measurement employing focused transducer and linear array mounted in a pitch-catch arrangement is considered. We present the wave theory of the system and demonstrate that the spatio-temporal spectrum of the output data set can be expressed as a product of the reflectance function of the liquid-specimen interface and overall transfer function of the system. By processing data in the spectral domain, it is possible to obtain parameters of dispersive waves. Using the wave model, it was shown that the angular resolution of the system increases with increasing of the number of the elements of the array and depends on the tilt angle of the array. Also, the problem of spatio-temporal spectrum aliasing was considered, and the maximal value of the pitch of the array was estimated at a given tilt angle of the array and directivity of the transmitting and receiving transducers. The results of the theoretical consideration were confirmed by the test experiments carried out in the 20 MHz frequency range

Suppression of Edge Waves by Apodization of Wide Band Cylindrical Transducers

Cylindrical wide band transducers are widely used in the V(z) and the V(x) methods for the analysis of elastic properties of solid materials. In the V(z) method1, the output voltage V of the focused transducer is acquired as a function of the defocusing distance z. Two cylindrical transducers are employed in the V(x) method2,3. Foci of the transducers are adjusted to be parallel to each other and to the specimen surface, and V(x) data are acquired during a scan of the receiving transducer along the specimen surface.

IN‐LINE ULTRASONIC INVESTIGATION OF SPOT WELD QUALITY USING MULTI‐TRANSDUCER SET‐UP

This article presents one of the most recent developments in real‐time ultrasonic quality control methods for resistance spot welds. Currently existing in‐line systems use single‐element transducer to characterize the spot weld quality. The new set‐up is based on 8 ultrasonic transducers placed in one line above the center of the spot weld. The solution presented in this paper makes another step forward towards improvement of accuracy of measurements using array of ultrasonic transducers.