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Vol 53, No 2 (2017)
- Year: 2017
- Articles: 10
- URL: https://journal-vniispk.ru/1061-8309/issue/view/11297
Acoustic Methods
Estimating the strength of welded hull elements of a submersible based on the micromechanical model of temporal dependences of acoustic-emission parameters
Abstract
A nondestructive technique for evaluating the strength of hull elements of submersibles is described. The technique is based on the micromechanical model of temporal dependences of the parameters of acoustic emission that is registered under an original novel technique of loading of a cylindrical hull section. The technique is also suitable for assessing the information value of resource-related acoustic-emission diagnostic indicators.
89-95
Analysis of errors in location of flaws in multipass welds using different clustering methods
Abstract
Titanium and duralumin inserts were introduced into a weld to imitate welding flaws in St3 steel samples. Analysis of the accuracy of locating the introduced flaws with different clustering methods (by digitized shape, main informative parameters, the rise rate of leading-edge envelope) has shown that these methods involve considerable time expenditures. The developed dynamic clustering has been combined with the clustering by main informative parameters and allowed in situ location of flaws during welding, while the weld has not been completed yet.
96-103
Electrical Methods
Development prospects for nondestructive testing of heterogeneous nonmetallic materials by the parameters of electrical response to a shock action
Abstract
Theoretical and experimental research has been conducted into the mechanisms of generation of electric fields under elastic shock excitation of heterogeneous nonmetallic materials that contain two types of mechanoelectric transductions, viz., double electrical layers at interphase boundaries and piezoelectric inclusions. Using the example of electrical responses from samples of heavy- and light-weight concretes and based on numerical modeling results, prospects are shown for using this phenomenon in nondestructive testing of heterogeneous nonmetallic materials that do not contain piezoelectric inclusions, e.g., layered and reinforced ones.
104-110
111-116
Evaluating parameters of semiconductors from their microwave reflection spectra in a wide temperature range
Abstract
The possibility has been shown for determining the thickness, conductivity, effective mass, carrier scattering coefficients, and concentration and activation energy of semiconductor-layer impurities based on measurement of the frequency dependence of the reflectivity of electromagnetic microwave radiation at different temperatures. A procedure for solving the inverse problem is described.
117-125
Magnetic Methods
Evaluating the structure of a ferromagnetic material based on magnetic-field strength between the poles of an attached two-pole magnetizing device
Abstract
The possibility for using a magnetic structoroscope with a two-pole permanent-magnet magnetizing device to test mechanical properties of stressed-deformed state of articles made of ferromagnetic materials has been investigated. Dependences of equipment readings on the geometrical dimensions of the structuroscope sensor and on the deformation of ferromagnetic material of a sample in tension in the elastic loading–unloading domain are presented for samples made of different ferromagnetic materials.
126-133
Radiation Methods
Estimating the efficiency of two algorithms for segmentation of digital radiation images of test objects
Abstract
A mathematical model that describes digital radiation images of test objects is presented. Two algorithms are given for automatic segmentation of digital images distorted by additive noises. The efficiency of the algorithms is estimated based on mathematical modeling.
134-141
Thermal Methods
Improved active contour modelling for isolating different hues in infrared thermograms
Abstract
Thermograms are widely used in industries and medicine for quality assessment and diagnostics. Thermogram analysis involves isolating desirable Regions of Interest (RoIs) and characterizing them in terms of physical parameters. Conventionally, image segmentation techniques are developed to extract a specific Region of Interest. However, an efficient algorithm that could segment any desired Region of Interest is yet to be developed. In this study, an efficient color image segmentation technique for isolating RoIs (in infrared thermograms) is developed by using Improved Active Contour Modeling (I-ACM). Two different techniques namely thresholding and region growing, have been used for mask selection in order to increase the segmentation ability of the algorithm. The performance of the proposed techniques is measured in terms of error and computational complexity. A user friendly GUI has been also developed for computer-aided analysis.
142-147
Ultrasonic Methods
The effect of water-cement ratio on acousto-ultrasonic characteristics in mortar
Abstract
A self-improved and debugged acousto-ultrasonic system was used to investigate the effect of water cement ratio (w/c ratio) on ultrasonic pulse wave propagation and find more accurate and effective evaluation parameters than the traditional ultrasonic pulse velocity (UPV). An experimental study on the uniaxial compression test and acousto-ultrasonic test of mortar cylinder with different w/c ratios (0.4, 0.5, 0.6) was presented. The results showed that the increase of w/c ratios deteriorated the mortar mechanical properties with the compressive strength decreased and reduced the UPV. The high w/c ratio also leaded high attention of wave amplitude and energy. Through analysis of the ultrasonic pulse waveforms, the maximum peak amplitude (AE parameter) couldn’t reflect the real change of the waveforms. The parameter energy, which is mainly determined by the average amplitude, showed a higher sensitivity to the mortar w/c ratio and more accurate reflection of the changes of the waveforms with different w/c ratios. Compared with other parameters, the energy could be used to evaluate the cement based material properties changes caused by the changes of composition and external effect.
148-158
Water content and temperature effect on ultrasonic pulse velocity of concrete
Abstract
In this paper, water content and temperature effect on the ultrasonic pulse velocity (UPV) of concrete was investigated. A series of tests were performed to examine the relationship between water content and UPV of concrete with different aggregate mixture proportions. Cube test specimens were made of concrete with water-cement ratio of 0.5. The concrete specimens were immersed in water for 90 days to saturate them. To measure the effect of different water contents on UPV, the test specimens were dried gradually to change the amount of water between measurements. This process was repeated until the concrete pieces was completely dried and weight no longer changed. The water content could be changed from about 6 to 0%. Following, another test procedure was conducted to research the relationship between temperature and UPV. To measure the influence of various temperature on UPV, completely dried concrete specimens were firstly cooled to –18°C and gradually heated to +180°C. In these two different procedures, the UPV values corresponding water content and temperature in the relevant ranges were periodically measured. The test results indicate that the increase in both water content and temperature increases almost linearly UPV of concrete. Based on correlation derived from the test data, irrespective of concrete properties a further increase in both water content of 1% and temperature of 10°C increases UPV of average 160 and 34 m/s, respectively. As overall assessment, this study demonstrates that the UPV is a function of both water content and temperature, and the changing of these two parameters has an important influence on ultrasonic pulse velocity of concrete.
159-166