Vol 55, No 3 (2019)
- Year: 2019
- Articles: 11
- URL: https://journals.rcsi.science/1061-8309/issue/view/11368
Acoustic Methods
An Amplitude-Phase Method for Testing Acoustic Contact of Ultrasonic Transducer
Abstract
A method is proposed for testing the acoustic contact of an angle ultrasonic transducer by measuring the amplitude and phase of an ultrasonic-wave signal received by an additional transducer from the working surface of the acoustic prism. The characteristic oscillograms of the change in the acoustic-contact quality signal as a function of the change in the contact area are provided.
Influence of The Passband of Frequency Filters on the Parameters of Acoustic Emission Pulses
Abstract
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.
Acoustic-Emission Testing of Vertical Steel Tanks in Hard-To-Reach Areas of the Far North
Abstract
The long-term safe operation of vertical steel storage tanks (VSSTs) for petroleum products in remote regions of the Far North implies objective timely detection of various types of emerging and existing defects with further provision for the monitoring of their development. The poor infrastructure and climatic features of the northern regions, as well as the time and material resources spent on preparing the standard scope of VSST testing adversely affect the performance and quality of its implementation. Therefore, taking these circumstances into account, a different approach is needed to inspect VSSTs operating in the hard-to-reach regions of the Far North. Taking the peculiarities of operating VSSTs at low temperatures in the Far North into account and based on the analysis of emergencies and accidents resulting from the degradation of VSST metal structures, the sources of damage are identified, the main problems of detecting planar flaws leading to catastrophic failures of VSSTs are shown, and a modified method is proposed for the local loading of bearing VSST members when conducting their acoustic-emission (AE) testing.
Recognition of Incipient Defects in the Units of Ship Machinery by Vibrodiagnostics Based on Optimum Decision Rules
Abstract
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.
Identification of Localized Void Defects in Composite by Recurrence Quantification Analysis of Ultrasonic Backscattered Signal
Abstract
Voids usually have a detrimental effect on the performance of carbon fiber reinforced polymer (CFRP). This paper presents a nonlinear dynamic method, known as recurrence quantification analysis (RQA), for the identification of localized void defects. First, five standard CFRP specimens with known porosity ranging from 0.2 to 5.94% are tested using ultrasonic pulse-echo technique, and the obtained backscattered signals are subsequently analyzed by RQA. The result shows that two RQA characteristic parameters, the recurrence rate and the Shannon entropy, both clearly increase with increasing porosity. Next, the RQA is performed on another CFRP specimen with unknown porosity. Two regions in this specimen containing localized void defects are detected based on the above finding. This result is finally verified by a destructive experiment. The research demonstrates that RQA is an effective new method for the identification of localized void defects in CFRP.
Damage Evolution Analysis of Mortar with Different w/c Ratio by Acoustic Emission Technique
Abstract
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.
Electromagnetic Methods
Eddy-Current System for Testing Inner Diameter of Pipes
Abstract
We propose a method for eddy-current testing of the inner diameter of electroconductive pipes. The design of an eddy current transducer is described, as well as an algorithm for converting measurement information signals and the block diagram of a system for testing the inner diameter of pipes that allows testing under conditions of significant radial displacements of the eddy current probe inside the pipe. The effectiveness of the proposed engineering solutions is evaluated.
Detecting Extended Complex-Shaped Defects in Electroconductive Plates Using a Magnetic Carrier
Abstract
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.
Magnetic Testing of Stressed State of Hydrotested Gas-Separator Wall
Abstract
The stressed state of a hydrotested gas separator has been studied by magnetoelastic demagnetization. Correlation dependences are obtained between the level of magnetoelastic demagnetization of a complex-loaded gas-separator wall and the magnitude of hoop, meridian, and equivalent stresses it experiences. The magnetoelastic demagnetization of a residually magnetized test-object wall, loaded with internal pressure, was estimated from the change in the strength of its magnetic stray field measured along the normal (Hn) and tangent (Hτ) to the surface. It has been established that the growth of mechanical stresses in the separator wall to half the value of the yield strength of steel it is made of causes a noticeable irreversible decrease in the normal (Hn) and tangential (Hτ) components of the strength of its magnetic stray field in the residually magnetized area. It is shown that the method of magnetoelastic demagnetization has the highest sensitivity to mechanical stresses and is easiest to implement and most prompt compared with coercimetry and tensometry.
Study of a Finite-Element-Based Spatial Distribution Model for Coal-Mining Wire-Rope Detection Signal
Abstract
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.
Thermal Methods
Active Thermal Testing of Delaminations in Heat-Shielding Structures
Abstract
We describe possibilities offered by active thermal testing when detecting delaminations of heat-shielding coatings from a metal base using an optical thermal-stimulation source that implements heating in a scanning mode. Results of numerical simulation of thermal processes are given for various defective situations. The thermophysical characteristics of heat-shielding materials have been experimentally determined, and the limits of the thermal method have been estimated for heat-shielding thickness and defect size.