A. Ptchelintsev

Ultrasonic Imaging with 2D Matrix Transducers

This paper has discussed a broad range of experimental results relating to development of 2D matrix transducer technologies and its potential applications. The major criterion for the imaging capability of the system generally depends on the penetration depth of the transducer and resolution. The influence of the various parameters, including various interface conditions, on the quality of the ultrasonic imaging is an important issue of this research and the goal for the further study. A more detailed analyses and experimental works taking into account those results are underway.

Monitoring of pulsed ultrasonic waves’ interaction with metal continuously heated to the melting point

A resistance spot welder has been equipped with embedded ultrasonic transducers. Using this setup for ultrasonic data acquisition during welding and a feature analysis promising results are reported. The technology discovers a large potential for nondestructive investigation of thermoelastic behavior of welds.

Method of quantitative evaluation of elastic properties of metals at elevated temperatures

A resistance spot welder has been used to evaluate the sound velocity in various materials at elevated temperatures. The method is indirect and its accuracy in the full temperature range strongly depends on the accuracy of the modeling. It provides a relatively simple setup to evaluating the elastic properties of metals, their alloys, and compounds in the molten state.

Ultrasonic 2D matrix PVDF transducer

During the past decade a substantial amount of work has been done in the area of ultrasonic imaging technology using 2D arrays. The main problems arising for the two-dimensional matrix transducers at megahertz frequencies are small size and huge count of the elements, high electrical impedance, low sensitivity, bad SNR and slower data acquisition rate. The major technological difficulty remains the high density of the interconnect. To solve these problems numerous approaches have been suggested. In the present work, a 24×24 elements (24 transmit+24 receive) matrix and a switching board were developed. The transducer consists of two 52 μm PVDF layers each representing a linear array of 24 elements placed one on the top of the other. Electrodes in these two layers are perpendicular and form the grid of 0.5×0.5 mm pitch. The layers are bonded together with the ground electrode being monolithic and located between the layers. The matrix is backed from the rear surface with an epoxy composition. During the emi...

Quantitative Nondestructive Evaluation Techniques for Investigation of Very Thin Coatings

Coatings are widely used in industry. They provide good electrical conductivity, wear resistance, thermal and electrical insulation, and corrosion protection. Recently submicron range coatings and sophisticated layered composite structures have emerged from the high technology advanced research. A nondestructive evaluation (NDE) of coatings has an immediate goal to ensure satisfactory properties of coated metals, and save often expensive materials. For this purpose two most powerful methods acoustic microscopy and eddy-currents have been used in industry for many years. Two techniques for NDE of micron and sub-micron range coatings by both methods are given in this paper; performance, advantages and limitations are outlined. There are a number of quantitative acoustic microscopy (AM) methods for investigation of thin layers, in this work one of them is discussed. The Doppler continuous wave scanning acoustic microscope has been used for the evaluation of 0.3–5.0 γm thick titanium nitride coatings on steel substrate. Thickness errors are typically within 10 percent. The method has an obvious advantage for nonconductive coatings and substrates and for coatings only slightly different in mechanical properties from the substrate, as nitrogen implantation hardening layers. This potential of the method has been illustrated on tool steel samples having a 0.2 μm thick nitrogen implantation coating. Eddy currents (EC): Operating at a single frequency, using various coils, thickness of conductive coatings on conductive and nonconductive substrates has been determined. Analytical solutions obtained for long coils and surface coils, are mathematically very compact, and allow a real-time evaluation. Aluminum foils of 32–64 μm thick, 0.3–0.8 μm thick metal films sputtered on nonconductive substrates, 15–45 μm thick aluminum coatings on stainless steel, and 2.8–58.5 μm thick zinc coatings on steel substrate have been measured. Agreement between theory and experiment is excellent. Discrepancies between the eddy current thickness and that determined using other methods are typically within few fractions of micron. Encountered problems with measurements on sub-micron range coatings are reported.

The acoustical monitoring of internal delaminations in fiber reinforced composites

The samples of carbon-fiber-reinforced composite materials with artificial impact damage was tested by pulse-echo acoustical methods. Combination of B-scans and C-scans represents the complete performance about size and position of delamination. The complex multi-layer structure of impact damage is shown in detail. The 3-D image of the delamination is created from the set of B-scans. Using a 2D array transducer gives us the possibility of fast testing of real parts in field conditions.

Precision measurement of thickness and conductivity of circular and plane products with Eddy current metrology

We report here the following topics of a quantitative nondestructive evaluation using eddy currents: cross-section measurements of long conductive products; measurement of the wall thickness and conductivity of conductive non-magnetic tubes; measurement of the thickness and conductivity of foils. On non-magnetic circular rods and tubes, and accuracy of the cross-section measurement was better than 0.3%. for hexagonal and square profiles, the accuracy was typically within 2%. Measurements performed on copper wires (empty set 0.9-1.5 mm) at 1 MHz implied errors on diameter determination typically lower than 4 mu m. Experiments on circular steel rods and wires (empty set 0.9-13 mm) in presence of the magnetic field H=40000 A/m have shown the accuracy of the diameter measurements better than 40 mu m. Experimental tests for brass and copper tubes (empty set 12-20 mm) with nominal wall thickness from 0.9 to 2.5 mm were carried out. Thickness was typically determined with a 2% accuracy simultaneously with a tube electrical conductivity. An uncertainty on conductivity measurements lower than 5% is obtained. An eddy current method based on the theoretical model of two-conductor line placed above a plane conductive medium is also developed. Copper and aluminium foils having thicknesses 15-200 mu m are studied experimentally in the frequency range 5-100 kHz. The uncertainty of the conductivity and thickness measurement better than 2% typically within 1% is obtained.