Том 55, № 3 (2019)

To study the effect of the passband of a digital filter on the nature of the attenuation of the amplitude of an acoustic emission (AE) pulse and on the change in the group velocity of a wave packet in the near zone of up to 300 mm from the radiation source, studies were conducted on a multilayered polymer-composite-material (PCM) panel and an AMG-2 aluminum alloy plate with a thickness of 6 mm. In the course of the experiments, it has been established that narrowing the passband of the digital filter from 30–500 to 100–200 kHz can significantly affect the accuracy of the coordinate location of AE-event radiation sources situated near AE transducers, at a distance of less than 100 mm. As the passband of the digital filter narrows and the low- and high-frequency components of the spectrum are cut off, the wave front of the recorded pulse becomes more gently sloping, resulting in an increase in the difference of arrival times (DAT) of pulses to the AE transducers and in a decrease in the calculated group velocity of the wave packet. The error arising in this case is greater than the passband of the filter applied.

We developed a method for revealing incipient defects in ship machinery during vibration-based inspection, based on studying the statistical properties of diagnostic features in the vibroacoustic signals of ship mechanisms and on the principles of the pattern recognition theory. The following applied solutions of the problem are obtained; an algorithm for constructing references for multidimensional feature spaces allocated in vibroacoustic signals and characterizing incipient defects in mechanisms for various modes (states) of their operation in the form of conditional multidimensional probability densities; an optimum decision rule for recognizing faults-incipient defects-and intact states of mechanisms, taking changes in the dimensionality of the feature spaces into account. The developed method has been verified experimentally in bench vibroacoustic and field tests of ship machinery.

In this paper, mortar specimens with different w/c ratio were tested under axial compression. The damage progress was monitored by acoustic emission (AE) technique and AE signals were collected. AE characteristics of mortar specimens with different w/c ratio are studied and the damage evolution process is analyzed by AE amplitude, peak frequency and AE N/E ratio (cumulative hits/cumulative energy). Under different w/c ratio, variation trend of the ratio of AE cumulative hits number to total AE cumulative hits number (AE cumulative hits number ratio) in each amplitude and frequency band is generally consistent, what’s more, AE cumulative hits number ratio in each frequency band and amplitude band at different stress level are studied. Distribution variation trend of AE cumulative hits number ratio in each amplitude and frequency band changing with the stress is generally consistent. When AE cumulative hits number ratio significantly increases sharply, it indicates that the mortar specimen will be destroyed. The damage evolution progress of mortar specimens with different w/c ratio under axial compression is analyzed by AE cumulative hits number ratio in each frequency band and amplitude band at different stress level and AE N/E ratio.

We studied oscilloscope waveforms picked up from a magnetic head scanning a magnetic carrier with the recordings of the spatial distributions of magnetic fields due to artificial complex-shaped defects in the form of cuts in plates made of aluminum, lead, and copper. The defect opening was 10–100 μm, and the plate thickness was 60 μm or more. The defects were exposed to magnetic field pulses with a rise time in the range of 1.5–50 μs, while recording fields due to defects on a magnetic carrier. The strength of a primary magnetic field, created by a flat inductor, varied in the range of 5–30 kA/m. We provide photographs of plates with defects and dependences of the electric voltage U (y) on y-coordinate, read from an induction magnetic head scanning the magnetic carrier with the records of fields due to defects in plates of different thickness and at different heights above the plates. Based on the conducted research, conditions have been established for identifying screened-from-view extended complex-shaped defects in objects in the form of aluminum, lead, and copper plates. A method of pulsed magnetic testing of extended complex-shaped defects in these objects has been developed. The method allows recording instantaneous distributions of magnetic field across an area of 10 cm² or more with a resolution in the measurement plane of 0.01 mm², with pulsed magnetic fields due to defects displayed on monitor screen by constructing the records of U (y) in a plane that corresponds to the test-object surface. These results can be used for express detection of continuity defects in electrically conductive objects, as well as when studying various magnetic and electromagnetic methods of testing.

Owing to inadequacies in the current technology for coal-mining wire-rope detection, a spatial distribution model for the coal-mining wire-rope detection signal based on a finite element analysis (FEA) is proposed. First, the three-dimensional FEA model for the coal-mining wire-rope-defect detection signal was developed to analyse the spatial characteristics of the magnetic flux leakage (MFL) signal of the coal-mining wire rope. On the basis of the results, the FEA model was experimentally validated. The experimental and FEA model results exhibited consistent patterns of change, and the research methods used in this study were demonstrated to be feasible. Lastly, the experimental prototype equipment was tested through simulation and experiments. The results show that compared with the conventional defect detection equipment, the new-type equipment detected 7 defects accurately in the experiment while the conventional equipment missed two. The signal-to-noise ratio of the new equipment is 33.1 dB higher than that of the conventional one, which reveals that it presents a better detection effect.