R. V. Kontsov

Ultrasonic structural probing of products based on materials with a complex structure by analyzing the statistical characteristics of the structural noise

It is shown that during ultrasonic control of products that are made of materials with a complex structure (cast iron, concrete, and bronze) the use of ultrasonic signals with a wavelength that is comparable to the sizes of the acoustic irregularities in a material induces the combined reflection of an ultrasonic probing signal from structural irregularities, which masks the reflections from the initial defects of the product. The combined reflected signal is correlated with the probing signal; in ultrasonic defectoscopy of products it has to be considered as interference that masks the echo signals from the initial defects of the product. At the same time, it provides information on the structural state of a studied material. In this work we consider the model of a complex material with a random structural irregularity distribution, for which the statistical characteristics of the combined reflected signal, viz., the density of the structural-noise probability, dispersion, and energy spectrum, are determined. We propose a new method for defining the structural state of a complex material by analyzing the statistical characteristics (energy spectrum and dispersion) of the structural noise.The experimental results on the analysis of the statistical characteristics of the structural noise are discussed for cast-iron products, allowing the structural state to be detected and monitored during their operation.

Choosing parameters of space-time signal processing in ultrasonic structuroscopy of cast-iron molds subjected to thermal cycling

It is shown that in order to improve the accuracy of measuring the speed of ultrasonic vibrations in cast-iron products by echo-pulse method, one should use noise-immune space-time echosignal processing methods that improve signal–to–pattern-noise ratio. Signal parameters should also be adapted for characteristics of the test object. Requirements for the choice of probing-signal parameters have been established as well as optimum displacement step of a double-crystal transducer. The value of the speed of ultrasound at a time moment that precedes the destruction of cast-iron mold has been determined.

Adaptive instruments for ultrasonic nondestructive testing of large objects with complex structures

An ultrasonic multifunctional adaptive measuring complex, which is built on the basis of a personal computer and algorithmically generates various simple and complexly modulated probing signals, is described. This system implements various radio-engineering algorithms for processing echo signals (storage, optimal filtering, synchronous detection, etc.) and provides adaptation of the signal parameters to the characteristics of inspected objects. Using the example of a frequency-modulated signal, it is shown that an adaptive measuring complex can increase the testing reliability and provide high sensitivity and high resolution owing to both the adaptive adjustment of the parameters of a probing signal and the compensation for distortions in the received signal in the electroacoustic path.

Choosing Phased Array Pitch in Ultrasonic Tomography of Materials with Inhomogeneous Structure

The influence of phased array (PA) pitch on signal/pattern-noise ratio when probing objects with inhomogeneous structure by low-aperture transducers of transverse acoustic waves is considered. A saturation phenomenon has been discovered for small PA pitches. The phenomenon is due to the influence of positive cross correlation between pattern-noise instances at neighboring receiving transducers. The optimum PA pitch has been determined to be approximately 0.5 of the wavelength when probing the object area across the PA and 0.4 of the wavelength when probing areas at the side of the PA. Experimental research has been carried out and proved the validity of the theoretical results.

Pattern-Noise in Ultrasonic Inspection of Articles Made of Complexly Structured Materials

Pattern-noise (PN) that occurs due to combined reflection of an ultrasonic probing signal from acoustic inhomogeneities in the material structure is an interference that conceals echo-signals from flaws. The most efficient method for extracting echo-signals from PN is multichannel spacetime signal processing (STSP). Different inspection purposes dictate different configurations of STSP schemes with the parameters that are determined by PN correlation characteristics. A theoretical model has been used to determine mutual PN correlation characteristics for the main types of transducers. The theoretical results have been confirmed experimentally.

Using antenna arrays for reference-free measurement of speed of ultrasound and thickness of concrete articles

A reference-free method is considered for concurrent measurement of the speed of ultrasonic vibrations and the thickness of concrete constructional products with ultrasonic antenna arrays that use the “focusing to a plane” algorithm.

Application of synchronous detection for ultrasonic thickness gauging of concrete Articles with a nonuniform Structure

Some problems that are encountered in the ultrasonic pulse-echo thickness gauging of large concrete building structures with high frequency-dependent ultrasound attenuation and a complicated nonuniform structure are considered. It has been shown that ultrasonic signals with complex modulation with further optimal filtering of echo signals should be used in single-channel testing to increase the sensitivity during the testing of concrete articles and to enhance echo signals in the presence of white noise. Synchronous detection of echo signals is advisable to increase the precision of measurements. Multichannel spatial–temporal signal processing via thickness measurements at several neighboring points of an article and further coherent summation of partial measurement results should be used to enhance ultrasonic echo signals in the presence of structural noise. However, it is recommended that the multichannel testing of concrete articles with a nonuniform volumetric distribution of physicomechanical properties be performed with the summation of partial echo-signal envelopes after their synchronous detection due to the broad spread of ultrasonic signal velocities in neighboring regions.