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Vol 54, No 1 (2018)
- Year: 2018
- Articles: 9
- URL: https://journals.rcsi.science/1061-8309/issue/view/11320
Acoustic Methods
Experimental Ultrasonic Study of the Elastic Modulus of Glass Fiber Plastics in Constructions
Abstract
Results of experimental study of the elastic modulus of composite polymer materials (glass fiber plastics) by a pulsed ultrasonic method are considered. Results of the in situ elastic-modulus testing in isotropic, transverse-isotropic, and orthotropic glass fiber plastics in articles and constructions are presented. A significant distinction between a dynamic elastic modulus determined by the speed of ultrasound and a static one measured according to GOST (State Standard) 9550-81 is demonstrated. Results of studying the anisotropy of fiber glass plastics are provided.
1-16
Pattern-Noise in Ultrasonic Inspection of Articles Made of Complexly Structured Materials
Abstract
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.
17-30
Decreasing Pulse Duration at Receiver Output under Emitter Excitation with Complex Waveforms
Abstract
The pulsed operation mode of an emission–reception system consisting of two immersion piezoelectric transducers separated by a liquid (glycerine) layer has been studied. Identical piezoceramic plates were used as active elements in the emitter and receiver. The rear sides of the plates were loaded on air. The emitting transducer was excited by composite-waveform electric signals consisting of two sine-wave half-periods with different amplitudes (with their sign taken into account). The length of each half-period corresponded to the half-period of emitting plate vibration at the antiresonance frequency. The first half-period was the exciting one, with the second, supplied at the appropriate moment, being the compensating one. The amplitudes of the compensating half-periods were precalculated based on a mathematical algorithm developed by the authors in their previous works. It has been shown that applying composite-waveform signals allows one to considerably reduce the duration of a signal at the receiver output as compared with the case where the emitter is excited by an electric pulse in the form of one half-period of vibration at the antiresonance frequency. Experimental data are in fair agreement with computation results.
31-36
Acoustic Evaluation of the Stress-Strained State of Welded Carbon Steel Joints after Different Modes of Heat Input
Abstract
The following problems are being solved within the framework of the “Long-Term Development Program of the Russian Coal Industry for the Period of up to 2030”: the modernization and renewal of coal production facilities and achieving the world standards of industrial security. The article is dedicated to the problems of evaluating the possibility of determining the stress-stained state (SSS) of the new elements of mining equipment in heat affected zones by acoustic and electron-microscope investigation.
37-43
Instantaneous Frequency Estimation for Motion Echo Signal of Projectile in Bore Based on Polynomial Chirplet Transform
Abstract
Microwave interferometer is one of the devices for measuring the movement travel–varying or time-varying velocity of projectile in bore. Microwave interferometer first obtains the Doppler echo signal including the motion information of the projectile in bore, then the velocity is measured based on instantaneous frequency estimation (IFE) of the processed and transformed signal. The parametric time-frequency analysis method can make spectral energy of nonlinear frequency modulation (FM) signal concentrate at some range in the new transform domain. As the motion echo signal of projectile in bore (MSPB) is a nonlinear FM signal, it could be described by polynomial chirplet, one of polynomial FM signal modes, which is used to construct transform kernel for the signal. In this paper, Polynomial chirplet transform (PCT) method is proposed to analyze the simulation and experiment echo signals of projectile in bore. The estimation error and Renyi entropy are used to measure quantify of the time-frequency distribution. Compared with short-time Fourier transform (STFT) method and Wigner-Ville distribution (WVD) method, our results show that the PCT method has most powerful anti-interference performance and highest accuracy of instantaneous frequency estimation for the simulation signal, and lowest Renyi entropy of the instantaneous frequency estimation for the experiment signal. In general, the PCT method has powerful anti-interference performance and high time-frequency concentration and accuracy of instantaneous frequency estimation for the motion echo signal of projectile in bore.
44-54
Damage Processes of Steel Fiber Reinforced Mortar in Different Fiber Content Revealed by Acoustic Emission Behavior
Abstract
The performance of the cement-based materials could be improved by the incorporation of steel fiber, but the damage processes become more complex with different content at the same time. The acoustic emission (AE) technology can achieve the global monitoring of internal damage in materials. Under the axial compression load, the AE signals of steel fiber reinforced mortar specimens with different fiber content during the whole damage process were selected. The analysis of the damage evolution process, failure mode and damage degree were conducted by AE energy, RA value, AF value and b value respectively. It is found that the cement matrix cracked on the initial stage, the cracks further developed in the medium stage as well the fiber out of shape and the fiber were pullout on the last stage. The cumulative AE energy is proportional to the ductility of the material. The damage mode and damage degree can be judged by identifying the damage stage which obtained by the analysis of the AF value. It conducted that AE parameters can describe the failure processes due to it change monotonically with the progress of damage.
55-64
Electromagnetic Methods
Peculiarities of Changes in the Desired Signal of a Magnetic Anisometer under Rotation of Its Attachable Sensor
Abstract
The way the rotation and speed of the sensor in a permanent-magnet anisometer affect its readings when inspecting the stress-strained state of ferromagnetic articles has been studied. Regularities of changes in the longitudinal and transverse magnetic-field strength components during sensor rotation have been revealed. A degree to which both components depend on the rotation speed has been demonstrated.
65-69
Using Film Flux Detectors to Determine Properties of Conducting and Magnetic Objects
Abstract
The optical images of magnetic fields recorded with flux detectors are provided as well as the distributions of electric voltage U(t) across an inductive magnetic head as it scans a discrete magnetic carrier that contains recordings of residual magnetic fields resulting from a pulsed magnetic field acting upon the magnetic carrier with a test object. Procedures have been developed that make it possible to measure the distributions of magnetic fields and inspect objects made of conducting or magnetic materials, while enhancing the accuracy of measuring conductivity σ, magnetic permeability μ, the homogeneity of distributions of σ and μ, thickness, and the parameters of solidity flaws in these materials.
70-76
Tuning Out from Base Electric Conductivity in Conductive-Coating Thickness Gauging
Abstract
The thickness gauging of nonmagnetic metal coatings applied to nonmagnetic bases with tuning out from base electric conductivity is considered. A measurement technique that enables the tuning out in increased-locality measurements within a wide range of coating thicknesses is described. Results of computational and experimental research are provided. Optimum inspection parameters are analyzed.
77-83