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.
It has been shown that in order to increase the sensitivity of ultrasonic noncontact shadow testing of products made of polymer composite materials (PCMs), it is necessary, along with the well-known ...techniques (increasing the amplitude of the probing signal, using radio technical signal processing methods, employing highly sensitive electroacoustic transducers), to optimize the parameters of noncontact testing. Criteria have been established for choosing air gaps between the emitting transducer and the test object and between the test object and the receiving transducer, as well as criteria for choosing the duration of probing signals. Methods for increasing the reliability of testing the border regions of small-thickness PCM products are proposed. The results of automatic noncontact scanning of PCM products in the shadow mode using an adaptive measuring complex that allows the testing parameters to be adapted to each new tested product are presented.
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.
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.
The article considers a method of ultrasonic structural analysis of articles made of cast iron based on increasing the precision of the measurement of the velocity of acoustic vibrations through ...extraction of the ultrasonic bottom echo signal from the structural noise by means of space-time signal processing.
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.
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.
A new method of measuring the velocity of acoustic waves in large-size concrete products is considered, based on the use of eigenfrequency methods. It is shown that it is necessary to monitor the ...velocity at several points on the surface of the article with subsequent calculation of the degree of cross correlation of the experimental and theoretical spectral characteristics for each measurement.
