Acoustic Emission Test Results Research Articles

Characteristics and Evolution of Tectonic Fractures in the Jurassic Lianggaoshan Formation Shale in the Northeast Sichuan Basin

The features and formation stages of natural fractures have significant influences on the fracturing of shale reservoirs and the accumulation of oil and gas. The characteristics and evolution of tectonic fractures in the Lianggaoshan Formation in Northeast Sichuan were investigated based on outcrops, drill cores, geochemical data, and acoustic emission test results. Our results demonstrated that the fracture types of the Lianggaoshan Formation were mainly low-degree bedding-slip fractures, followed by high-degree through-strata shear fractures and vertical tensile fractures. The influences of strike-slip faults on the fractures were stronger than those of thrust faults; fractures in thrust faults were concentrated in the hanging wall. The densities of tensile and shear fractures were inversely proportional to the formation thickness, while the density of interlayer slip fractures was independent of the formation thickness. The density of tectonic fractures was proportional to the quartz content. The fractures of the Lianggaoshan Formation were generated in three stages during uplift: (1) Late Yanshan–Early Himalayan tectonic movement (72~55 Ma), (2) Middle Himalayan tectonic movement (48~32 Ma), (3) Late Himalayan tectonic movement (15 Ma~4 Ma). Fractures greatly improve the oil and gas storage capacity and increase the contents of free and total hydrocarbons. At the same time, they also reduce the breakdown pressure of strata. This study facilitated the prediction of the fracture distribution and oil and gas reservoirs in the Lianggaoshan Formation and provided references for the selection of favourable areas for shale oil and the evaluation of desert sections in the study area.

Effects of roughness on shear properties and acoustic emission characteristics of bonded Rock-Concrete interfaces

The shear properties of bonded rock-concrete interfaces play a crucial role in the analysis of engineering structures stability. In this paper, laboratory direct shear tests and acoustic emission (AE) tests are conducted on standard cylinder specimens with varying levels of rock surface roughness. The aim is to gain a better understanding of shear behavior and failure mechanisms of the bonded interface between rock and concrete. The results show that increasing of roughness enhances the brittleness and peak dilatancy characteristics of the specimens. However, the residual shear strength exhibits the opposite trend. In addition, the distribution of residual concrete on the rock surface changes gradually from localized spots to larger areas. The AE test results demonstrate the occurrence of peak AE peak energy and count generation during shear failure. The evolution of the AE-b value indicates that the macro-fracture surface of the bonded surface is the result of the repeated conversion between large and small-scale micro-cracks. Moreover, the fluctuation value of the AE-b value is not influenced by the roughness of the rock interface. Hence, in this experiment, the 90% fluctuation mean value is selected as the primary parameter for rupture warning. Furthermore, The distribution of RA-AF values reveals the generation of numerous tension-shear composite crack types during the fracture process. The number of shear cracks in the failure stage exhibits an increasing trend with increasing roughness.

The effect of signal-to-noise ratio value on the error in measuring acoustic emission parameters: statistical assessment

Modern acoustic emission diagnostic systems and complexes are a sensitive tool for detecting developing defects at an early stage when monitoring the technical condition of objects under operational loads. A significant limitation of the application acoustic emission method is the difficulty in isolating signals against the background of acoustic and electromagnetic interference. The effect of interference during acoustic emission recording significantly complicates the interpretation of parameters that characterize the technical condition of the test object. To increase the value signal-to-noise ratio and increase the reliability of the results of acoustic emission testing in the quantitative assessment of parameters, filtering methods are used. The subject of this study is the study of the effect of signal-to-noise ratio value on the measurement error acoustic emission parameters formatted during noise compensation using the polynomial filtering method. The basis of the statistical model characterizing the effect of signal-to-noise ratio value on the measurement error acoustic emission parameters is based on the machine learning method — linear regression. The dependence of the measurement error on the signal-to-noise ratio value was approximated by the least-squares method and visualized using a scattergram. It was found that when using the Butterworth filter, the relative measurement error acoustic emission parameters do not exceed 3 %, which are orders of magnitude lower than the values obtained for the Bessel filter and Daubechies mother functions 8 based on wavelet filter. A high inverse non-random correlation was established (r > 0.9), due to a decrease in the values of the relative measurement error emission parameters and an increase in the signal-to-noise ratio value. The developed statistical model describes the effect of the signal-to-noise ratio value on the value relative error in estimating the acoustic emission parameters. The adequacy of the developed model was confirmed by calculating the coefficient of determination and checking its statistical significance. It is shown that the use of Butterworth filter to compensate for interference significantly increases the information content of the results of measurements of acoustic emission parameters. The developed statistical model can be used in the development of new or improvement of existing complexes and systems for processing acoustic emission data to improve the reliability of the results of acoustic testing.

Variations in seismic parameters for the earthquakes during loading and unloading periods in the Three Gorges Reservoir area

As the largest water conservancy and hydropower project in China, the Three Gorges Reservoir is a weak seismic activity area before impoundment, but the frequency of earthquakes increases significantly after impoundment. The spatial density scanning method was used to obtain the characteristics of spatio-temporal earthquake distribution in the reservoir area during loading and unloading processes. The results show that the frequencies of earthquakes during the loading and unloading processes were higher than that during the low-water-level operation period, which is well explained by the acoustic emission test results. The seismic b-value, fractal dimension D, and spatial correlation length SCL can be used together to indicate stress criticality. To analyze the impacts of reservoir water loading and unloading on seismicity in the reservoir area, time-scan analyses were performed on the b-value, D-value, and SCL of earthquakes near the Zigui segment and the Badong segment. Previous studies argued that the time-varying characteristics of b-values do not hold predictive significance for earthquakes in the M4.0–6.2 range. However, our study found that the time-varying characteristics of b-values are of predictive significance for earthquakes around M4.0. These seismic parameters decrease significantly before moderate earthquakes but at different rates in different regions.

Research on Failure Precursor Based on Characteristics of Energy Dissipation Rate for Rock

Research on early warning of rock disaster based on the energy theory is closer to the essence of rock failure. In this paper, static compression tests and acoustic emission (AE) tests of coal rock under 0, 8, 16, and 25 MPa confining pressures were carried out on the MTS815 test system. Energy evolution law in the rock failure process was analyzed according to the relationship between mechanical parameters, AE parameters, and energy dissipation rate (EDR) in the rock failure process. Eventually, a new index for evaluating rock failure precursors was proposed based on EDR. The results show that the EDR has a good correlation with mechanical strength and AE events under different confining pressures. The deformation and failure characteristics of coal rock can be truly characterized by EDR. The variation of EDR can be divided into a quiet stage, a stable increasing stage, an active stage, and a stable stage. The EDR level in the quiet stage is obviously enhanced by confining pressure. When EDR reaches the peak, AE events increase rapidly. In the active stage, the EDR peak value is concentrated and large, the AE event is highly active, and stress drops abruptly, indicating that the EDR is reliable for evaluating the rock failure process. Compared with AE test results, it is found that the warning stress and warning time of the EDR failure precursor occur later than that of the AE failure precursor, and the former is closer to the peak stress of rock, which is more universal in engineering and could provide a better reference value for preventing rock disaster.

The influence of AlSi10Mg recycled powder on corrosion-resistance behaviour of additively manufactured components: mechanical aspects and acoustic emission investigation

The effects of using recycled AlSi10Mg aluminium alloy powders on the mechanical properties and the corrosion-resistance behaviour of the components manufactured via selective laser melting (SLM) were analysed. The microstructural results show that the utilisation of recycled powder causes coarsening of interdendritic Si-network, especially along the melt pool boundaries of the SLM specimens. The corrosion resistance of the samples was evaluated by means of neutral salt spray (NSS) tests for 1000 h and mass loss measurements. The corrosion behaviour, in terms of surface roughness, density and porosity, however, remains almost the same between the samples produced by virgin and recycled powder. In addition to this, a passive NDE tool has been used to investigate and study the impact of powders on the corrosion performance of the alloy: Acoustic Emission (AE) technique. SEM observations allowed to highlight the morphological differences in the surface of the test specimens induced by the exposure condition. Thus, it was possible to correlate the AE results to corrosion mechanisms activated on the surfaces of the test specimen. A good correlation between the corrosion-resistance behaviour and the AE test results were obtained. Finally, the mechanical properties before and at the end of the accelerated corrosion were evaluated according to the yield strength, tensile strength, and elongation at breakage. The results showed comparable mechanical properties for the samples produced using both virgin and recycled powders. Besides, no notable influence of the exposure to corrosive environment on the mechanical performance was observed.

Fracture Behavior of Permeable Asphalt Mixtures with Steel Slag under Low Temperature Based on Acoustic Emission Technique.

Acoustic emission (AE), as a nondestructive testing (NDT) and real-time monitoring technique, could characterize the damage evolution and fracture behavior of materials. The primary objective of this paper was to investigate the improvement mechanism of steel slag on the low-temperature fracture behavior of permeable asphalt mixtures (PAM). Firstly, steel slag coarse aggregates were used to replace basalt coarse aggregates with equal volume at different levels (0%, 25%, 50%, 75%, and 100%). Then, the low-temperature splitting test with slow loading was used to obtain steady crack growth, and the crack initiation and propagation of specimens were monitored by AE technique in real time. From the low-temperature splitting test results, SS-100 (permeable asphalt mixtures with 100% steel slag) has the optimal low-temperature cracking resistance. Therefore, the difference of fracture behavior between the control group (permeable asphalt mixtures without steel slag) and SS-100 was mainly discussed. From the AE test results, a slight bottom-up trend of sentinel function was founded in the 0.6–0.9 displacement level for SS-100, which is different from the control group. Furthermore, the fracture stages of the control group and SS-100 could be divided based on cumulative RA and cumulative AF curves. The incorporation of 100% steel slag reduced the shear events and restrained the growth of shear cracking of the specimen in the macro-crack stage. Finally, the considerable drops of three kinds of b-values in the final phase were found in the control group, but significant repeated fluctuations in SS-100. In short, the fracture behavior of PAM under low temperature was significantly improved after adding 100% steel slag.

Determination of nano characteristics of strength of materials based on the multilevel model of time dependences of acoustic emission parameters

While manufacturing and exploitation of different materials, there could be observed complex physicochemical processes of interaction between their individual components and these components with the environment. Revealing such mechanisms helps to understand their distinct features and optimize technological processes of manufacturing materials with certain characteristics. The solution could be based on interpretation of results of acoustic emission (AE) tests from the perspective of multilevel kinetic model of AE of heterogeneous materials. The article describes the research, the essence of which was to identify systematic changes in the values of the parameters of the AE coefficients included in the model when changing various technological and operational factors on the basis of their operational assessment based on the results of acoustic emission tests.

Self-healing of thermal cracks in asphalt pavements

As an intrinsic property of asphalt material, self-healing could reverse the cracking process in asphalt pavements and extend their service life. This study provides quantitative assessment of self-healing of thermally induced damage in asphalt concrete materials using Acoustic Emission (AE) as well as Disk-shaped Compact Tension (DCT) tests. Asphalt concrete specimens were subjected to eight cooling cycles and the effects of resting time between cooling cycles on self-healing were investigated. The AE test results showed gradual degradation in self-healing capability of asphalt mixtures as the material was exposed to increasing number of cooling cycles. In addition, AE results indicated that the 12 h resting time between cooling cycles significantly improved the self-healing by more than 30% and allowed the material to regain most of its self-healing capability. DC(T) results also showed that the fracture energies of asphalt mixtures were increased on the average by 13% due to the 12 h of resting time. DC(T) test results were consistent with the findings from the AE tests indicating that both approaches could successfully capture the effect of resting times on the material fracture properties.

METHODS OF ACOUSTIC EMISSION ESTIMATION OF NANO-CHARACTERISTICS OF THE STRENGTH OF STRUCTURAL AND ENGINEERING MATERIALS OF THE OBJECTS

The acoustic emission method is the most promising metrological basis for non-destructive testing of strength. The necessity of solving problems of acoustic emission prediction of fracture and the ambiguity of the connection of the results of acoustic emission tests makes the problem of modeling strength heterogeneity relevant; it suggests a transition to a more complex level of research. The complexity of predicting the behavior of heterogeneous materials necessitates modeling and determining the parameters of the fracture process at the nano-defining operational level and the need to interpret the Kaiser effect revealing the strength heterogeneity as a phenomenon of a decrease in the activity of elastic radiation upon application of repetitive loads on the object under control. Heterogeneity modeling requires determining of its type, criterion and approach to estimation. The type of heterogeneity depends on the solved problem and has to be associated with the property that determines the function of real objects. Also, the criterion should be informative and the method of its evaluation should be non-destructive. Examples of modeling the temporal dependences of the AE parameters under conditions of strength heterogeneity are given, the analysis is carried out and the Kaiser effect is estimated from the point of view of a multilevel model of the dependences of the temporal parameters of acoustic emission.

Методика неразрушающего акустико-эмиссионного контроля прочности сварных соединений

The article presents examples of implementing the nondestructive acoustic emission (AE) strength examination technique based on long-term prediction of welded joint fracture. The technique is developed on the basis of a micromechanical fracture process model and time dependencies of the AE accompanying the fracture process. The article describes the AE test results obtained by different researchers for various samples having different stressed-and-strain patterns, with butt and fillet weld joints and having different flaws appeared during the welding process and afterwards. Conventionally used diagnostic parameters (number of impulses, amplitude, average energy of the AE impulses recorded in the elastic loading stage, and the values of the local dynamic parameter), as well as sequentially calculated diagnostic parameters following from the proposed micromechanical model were used as information-containing indicators. The correlation coefficient between the values of AE diagnostic parameters or the strength characteristics calculated from them and the experimentally determined values of time to failure or to cracking, rupture load, stress level, and flaw sizes was adopted as the information content indicator. Comparison of different AE-based diagnosing versions has shown the advisability of using the proposed diagnostic parameters, which are invariant to the type of samples, type of recording devices, type of defects, types of loading, and the generated stressed state. The obtained results create prerequisites for achieving better efficiency of AE-based production-grade material examination technology.

Characterization of embrittlement temperature of asphalt materials through implementation of acoustic emission technique

The present study focuses on the application of an acoustic emission (AE) based laboratory test to evaluate low-temperature cracking performance of several types of asphalt materials in the context of a recently completed national pooled fund study on low-temperature cracking (LTC). Comparisons are made between AE test results and the critical cracking temperature of asphalt binders determined from Bending Beam Rheometer (BBR) test and Direct Tension Test (DTT), which are in turn compared to field observed thermal cracking in the corresponding test sections. Based upon our findings, recommendations are made as to the potential use of the AE-based technique in asphalt binder specification.

Use of acoustic emission testing in injection moulding process

This paper presents the experimental results regarding acoustic emission signals measured during the injection moulding of those standard test specimens commonly used for examining the shrinkage behaviour of various thermoplastic materials. The acoustic emission was measured on a new injection mould and injection mould with the visible cracks on the cavity's surface. Two resonant 150 kHz piezoelectric AE sensors were attached to tool steel inserts via AE waveguides. The results of acoustic emission testing on the crack defected tool steel insert revealed higher acoustic emission activity compared with that captured on the brand new engraving insert under same processing conditions. Specimens produced with a new and defected tool were scanned with an optical 3D digitiser. Results of the experiments confirm that acoustic emission measuring during injection moulding of polymer materials is promising technique to characterise integrity of injection moulding tool regarding occurrence of cracks.

A study on acoustic emission technology for tank bottom corrosion inspection

PurposeThe purpose of this paper is to report an investigation into acoustic emission (AE) characteristics of the corrosion situation of the bottom of a large storage tank.Design/methodology/approachGuard sensors were applied in on‐line AE inspection of a tank bottom, and the AE signal characteristics of the corrosion areas of tank bottom were analyzed. The AE test results were compared with those from an internal tank internal test.FindingsIt was observed that guard sensors could shield effectively a large proportion of the extraneous noise signals inside the tank. The characteristics of AE signals from different types of corrosion were significantly different. A comparison of AE test results and tank internal inspection data showed a good agreement.Originality/valueCharacteristic AE signals from different types of corrosion were obtained for the first time, which assisted in the identification of the tank bottom corrosion situation.

Results of acoustic emission tests of corrosion protection degree of ship steel tanks covered by means of protective coatings (Phase I)

This paper presents methods and results of the 1st series of tests of acoustic emission (AE) signals, aimed at assessing degree of corrosion protection of a tank made of hull structural steel, protected by means of a protective coating combined from polyurethane layer and concrete filler. The tests were carried out in compliance with a method specially elaborated for application to the work in question. In the method were used requirements of the standards in force, as well as experience gained during realization of the research project CORRSHIP, included in 5th Frame Program of European Union. The application of the AE method to detect and localize corrosion sources during exposure of specimens to corrosive mixture confirmed its high usefulness for the carried-out tests on corrosion protection effectiveness of new types of protective coatings.

Diagnostics of the predestruction state based on amplitude and time invariants of the flow of acoustic-emission acts

The method and results of diagnostics of the predestruction state are described based on deviations of the amplitude and time invariant relationships between the parameters of the flow of acoustic- emission (AE) acts and their stable values. The relationship of the AE invariant method with the methodology of the synergetic approach to the destruction of solids is shown. Amplitude invariant relationships of AE have been estimated both by tests of standard specimens of 15Kh2NMFA hull-plate steel and by the previous results of AE tests of a VVER-1000 reactor vessel.

Determination of the Effectiveness of Lubricants for Locomotive Bearing Units by Means of the Acoustic-Emission Method

The theoretical fundamentals and experience of using the acoustic-emission method for estimating the effectiveness of lubricants for bearing units is considered. The results of practical investigations of the effect of the presence and watering of lubricants on the acoustic emission of a bearing unit are given. It is proposed to go over to repressing the lubricant into the bearing unit on the basis of the results of acoustic-emission testing.

Acoustic emission testing of repaired storage tank

In order to check the structural defects of a repaired storage tank, acoustic emission (AE) signals were monitored during a load sequence of 90–110% maximum operating load range. Then, based on the AE activity indications, subsequent radiographic testing (RT) was conducted. The field AE test results showed the active emissions of weld-like defects and the inordinate emission bursts of mechanical noise signals. The mechanical noise resulting from valve shut-off was characterized by the high-density emissions of high-count events compared with the genuine emissions. Some activity indications were confirmed to be correlated with significant weld-like defects by the follow-up RT, but other emissions appeared to be unrelated to any detected defects. The observed weld-like defects were a through-wall weld crack of 1.5 cm length and a round individual porosity of 0.5 cm diameter, respectively. Under the 110% maximum operating load conditions of the repaired storage tank, the detected defect emissions were active but not characteristic of defect growth.

Fundamentals, advanced concepts of measurement and equipment, and results of acoustic emission testing (In German: English Abstract)

Fundamentals, advanced concepts of measurement and equipment, and results of acoustic emission testing (In German: English Abstract)