AE Signals Research Articles

STUDY ACOUSTIC EMISSION SIGNALS AT TENSION STEEL 20

An investigation was made of acoustic emission signals during uniaxial tensile testing of flat specimens of steel 20 used for parts of welded structures with a large volume of welding, as well as pipelines, collectors and other parts operating at temperatures from –40 to 450 °C under pressure. Tensile testing with simultaneous registration of acoustic emission was carried out on a universal testing machine manufactured by Tinius OIlsen Ltd, model H100KU, at a movement speed of the active gripper of 0.05 meters per minute. Registration of AE signals was carried out using wideband GT350 sensors from GlobalTest and an analog-to-digital converter NationalInstruments 6363X with subsequent storage of the registration results in the form of a time series in the computer memory. A comparative analysis of the amplitude distribution of the AE signal for the area of the yield area and the area of destruction was carried out according to the value of information entropy, fractal dimension, and self-organization parameter. It was found that the parameter of self-organization of the amplitude distribution of the signal is the most informative in describing the processes associated with acoustic emission. As additional information, it is advisable to use data on the structure of the self-organization parameter. The results obtained indicate the possibility of using the statistical model of the Dirichlet distribution as a model of processes associated with the appearance of acoustic emission signals from sources of incipient and developing defects during routine tests of products made of structural carbon high-quality steels with a pearlite-ferrite structure. The paper presents a version of the model and modeling algorithms for FE-modeling corrosion cracking processes in structural elements loaded by pressure and exposed to aggressive corrosion media. To assess the effectiveness of the present models and algorithms, the failure process of a thin-walled tubular specimen partly submerged into a chlorine-containing liquid and loaded by axial tension is numerically modeled.

Fine structures of acoustic emission spectra: How to separate dislocation movements and entanglements in 316L stainless steel

Intermittent avalanches in a multitude of materials are characterized by acoustic emission, AE, where local events lead to strain relaxations and generate shock waves (so-called “jerks”), which are measured at the sample surface. The bane of this approach is that several avalanche mechanisms may contribute to the same AE spectrum so that a detailed analysis of each individual contribution becomes virtually impossible. It is, hence, essential to develop tools to separate signals from different dynamical processes, such as ferroic domain switching, collapse of porous inclusions, dislocation movements, entanglements, and so on. Particularly, difficult cases are dynamical microstructures in fcc alloys where the AE signal strength is weak. Nevertheless, using profile analysis of AE signals, we can distinguish between two mechanisms, namely, dislocation movements and dynamic entanglements in fcc 316L stainless steel. In this approach, we are able to measure the statistical AE durations of both subsets separately. The fingerprint for superposed avalanches with different durations is seen by the scaling between the energy E and the maximum amplitude A of each avalanche E ∼ Ax with x = 2. While the same exponent x applies for both mechanisms, the scaling relation shows two branches with different absolute energy values. The two mechanisms are then confirmed by separating the energy distributions P(E) ∼ E−ε for the two mechanisms with ε = 1.55 for dislocation movements and ε = 1.36 for entanglements.

Monitoring of Burn Damage Occurrence under Different Grinding Conditions Using Acoustic Emission

This paper presents the effects of the operating conditions (i.e. cutting speed and the amount of infeed) in grinding on the occurrence of thermal damage to the workpiece. The paper commences with a brief background to the analysis methods. Firstly, the AE signals detected under different operating conditions are analysed in time and frequency domains. It has been found that an increase in cutting speed or feed rate increases the strength of AE activity which is clearly reflected by the statistical parameter. Moreover, the cutting speed rather than the feed rate is more influential on the occurrence of burn damage. When the cutting speed is increased, the workpiece has been damaged severely and the AE content around 86kHz is significantly reduced.

Experimental investigation of crack propagation behavior and failure characteristics of cement infilled rock

A detailed understanding of the failure characteristics of infilled jointed rock is a key concern in underground engineering and is critical to the design, construction and maintenance of relevant projects. In this paper, uniaxial compression tests were performed to investigate the effect of the joint arrangement (different rock bridge angles) on the strength and crack propagation of red sandstone containing a set of preexisting infilled flaws of the same sizes and angles, while the crack fracturing process was observed by AE and strain monitoring. When the angle between the rock bridge and loading stress was less than 24°, the rock mass failure form was tensile failure with some localized shear failure occurring in the rock bridge damaged by crack penetration, leading to an overall decrease in the carrying capacity. The turning points of the strain and AE signal were clearly observed to be caused by the initiation and propagation of cracks, and the energy consumed by the initiation of shear cracks was greater than that of tensile cracks. The study was further conducted using the fracture mechanics numerical code FRACOD to investigate the crack propagation law and failure mechanism under different loading stress conditions. Simulation results from three 2D similar models showed that the percentage of open fractures decreased, but slipping increased; in addition, the total length of the fractures was greatly reduced with increasing confining stress. These results are important and valuable for understanding the crack mechanism of rock engineering in deep underground mining excavations.

Cluster analysis of acoustic emission signals and infrared thermography for defect evolution analysis of glass/epoxy composites

In this paper, a combination of acoustic emission and infrared thermal imaging technology is used to study the defect evolution mechanism of Glass/Epoxy composites with bubbles and delamination defects under the single-shot tensile load. The analysis of the acoustic emission signal consists of the k-means method and principal component analysis (PCA). According to the clustering method, the amplitude and peak frequency of the AE signal are clustered. The results show that the AE signal can be divided into four clusters during the tensile loading process, which correspond to four different damage modes: matrix cracking, fiber/substrate stripping, delamination and fiber breakage. The characteristic frequency range of each damage mode was determined by cluster analysis. The effects of bubble defects and delamination defects on the structural strength of the composites were analyzed by experiments. In addition, the combination of acoustic emission and infrared thermal imaging technology can effectively monitor the defect location and damage trend of composite materials.

Investigation on the Effect of Dynamic Frequency on Fracture Evolution in Preflawed Rock under Multistage Cyclic Loads: Insight from Acoustic Emission Monitoring

This study is aimed at revealing the effect of dynamic loading frequency on the fracture evolution behavior in preflawed rock samples under multistage cyclic loading conditions. The fracture evolution characteristics were investigated using stress-strain descriptions and in situ acoustic emission techniques. It is shown that rock strength, deformation, AE pattern, and fatigue life are strongly affected by the applied dynamic loading frequency. Rock fatigue strength and lifetime increase with the increase of dynamic loading frequency. The AE count and energy output both increase with the increase of the applied loading frequency. Six kinds of cracking modes were revealed by AE spectral frequency analysis. It is shown that large-scaled cracks are easy to be formed for rock subjected to high-frequency loads, reflected as the deceasing of AE signals with high-frequency–high-amplitude signal feature. It is suggested that applied dynamic loading frequency has obvious impact on the crack coalescence at the rock bridge segment. The testing results are helpful to enhance the cognitive of the influence of dynamic frequency on the crack communication behavior and can be expected to predict the stability of rock mass structures where rock mass is subjected to fatigue loading.

Flank wear prediction in tungsten carbide tool using acoustic signal amplitude in conventional turning operation

A tool wear prediction system that senses the cutting tool wear and allows for the optimum utilization of the tool is a deciding factor in achieving good surface quality of machined products. In recent years, the use of acoustic emission signals that emerged during machining operations has gained great significance in accurately predicting the tool condition. The objective of this work is to determine the variation in acoustic signal characteristics with tool flank wear in conventional turning process using Fast Fourier Transformation (FFT). Unlike the previous works, the experiments in this work were performed after optimizing the distance of the sensor position from the tip of the tool, since the optimum position of the sensor determines the transmission of the acoustic signals with minimum attenuation. The obtained raw signal output of the acoustic sensor is processed using FFT and the spectral analysis of the signal is carried out to determine the frequencies and also the magnitude of signal content at each frequency. This study establishes a correlation between the flank wear and the amplitude of acoustic signals. The model is validated using three sets of experiments at various cutting conditions. The average percentage deviation of the predicted tool wear from the experimental results is found to be 9.97%. This study indicates that the AE signals can be used to model the flank wear progression and can be useful for the accurate flank wear prediction in machining processes.

Damage process in glass fiber reinforced polymer specimens using acoustic emission technique with low frequency acquisition

The damage process in fiber-reinforced polymers (FRP) has been the subject of continuous studies in recent decades using different approaches. In particular, the acoustic emission technique has been proved to be a powerful tool in the monitoring of structures of this type of material due to the large acoustic activity captured when this material is loaded to rupture. The present work explores several indexes that were calculated from the experimental recording of acoustic emission signals, and their efficiency in describing the failure process in structures. One of these indexes, called c value, is originally proposed, and its sensibility it is compared with other classical parameters that are usually employed in the Acoustic Emission analysis. A 3-point bending test has been performed on a glass fiber reinforced polymer plate. Our own methodology was proposed to identify AE signals in semi-automatic manner. This methodology also allowed a faster analysis of the global parameters during the process data of the AE test. The global parameter evolution obtained from the acoustic emission data during the damage process could be considered as precursors of the more meaningful event and as an aid to understand in which way the structure is going to the collapse.

Laboratory investigation of the temperature influence on the mechanical properties and fracture crack distribution of rock under uniaxial compression test

In order to study the influence of high temperature on the mechanical characteristics and crack distribution of progressive failure process of rock, the laboratory uniaxial compression experiments were carried out on sandstone treated with different temperatures (25–1000 °C), and the variation characteristics of stress, deformation, and acoustic emission parameters during the failure of samples were analyzed. At the same time, the fracture crack distribution and fractal characteristics were analyzed through the industrial computed tomography (CT) test of the failure samples. The results show that temperature can affect the deformation and strength characteristics of rock. The stress thresholds and elastic modulus appear to increase when the preheating temperature increases from 25 to 400 °C and decrease when greater than 400 °C. The activity of AE signal is positively correlated with temperature. The CT results confirmed that with increasing temperature, the fracture cracks in the failure samples changed from a small number of single fracture cracks to a complex and crisscross distribution of small cracks. The failure cracks gradually gathered in the middle of the samples. The box-counting dimension of the fracture crack is between 1.4060 and 1.7262, and higher preheating temperature corresponds to the larger box-counting dimension, indicating that the temperature increases the complexity of the fracture crack. This outcome shows that temperature has an important influence on the deformation and failure of rock.

Comparative multiscale investigations of material removal behaviors of SiCp/5083Al, SiC ceramic and 5083Al alloy by single scratch tests

To gain a deep insight into the material removal mechanism of high volume fraction SiCp/Al during a grinding process, comparative multiscale investigations of material removal behaviors of 50 vol% SiCp/5083Al, bulk SiC and bulk 5083Al are presented by single scratch tests. Scratch mechanical properties including scratch force, friction coefficient and AE signal, as well as cross-sectional profile including residual scratch depth and material removal ratio are introduced to measure material removal behaviors at macroscale and mesoscope. Moreover, surface morphology of scratch grooves with help of SEM micrographs and explanatory model of material removal mechanisms are used to understand material removal evolution at microscale. It has demonstrated that at macroscale and mesoscope material removal behaviors of SiCp/5083Al are similar to that for 5083Al, but different from that for SiC, at microscale essentially different from that for 5083Al and SiC. Normal force (scratch depth) has significant influence on material removal behaviors, a sufficiently low scratch depth could achieve ductile removal of particles SiC resulting in a comparatively good surface for SiCp/5083Al, otherwise, the reverse. The work findings provide a critical insight of the material removal mechanism for SiCp/Al by considering coupling effects of particles SiC and matrix Al, and critical information for improving grinding quality.

Fracture failure analysis of freeze–thawed granite containing natural fracture under uniaxial multi-level cyclic loads

Rock mass containing natural fractures is susceptible to freeze-thaw (F-T) weathering in cold regions and could result in the instability of rock engineering and even serious geological hazards. Yet the F-T action on the change of fracture physical characteristics and the associated fracturing evolution of naturally fractured rock is poorly understood. In this work, multi-level compressive cyclic loading experiments were performed to investigate the fracture evolution of naturally fractured granite using real time acoustic emission monitoring and post-test CT scanning. The results show that the aperture change of natural fracture is related to the fracture openness and filling characteristics, the open-type fracture is sensitive to F-T treatment and its aperture increases faster than the close-type and fill-type fractures. In addition, the stress strain curve pattern is impacted by the initial natural fracture volume. The AE activities at fatigue loading stage are weaker than the stress-increasing stage. The proportion of low frequency AE signals increases with increasing natural fracture volume, and the shear-sliding along natural fracture results in the occurrence of low-frequency signals. Moreover, interactions between the natural fracture and stimulated new fracture are visualized using CT scanning and it is found that the initial natural fracture volume impacts the failure mode and fracture network pattern. The testing results are expected to improve the understanding of the influence of natural fractures on rock damage and deformation in cold regions.

The determination of the information frequencies in the frame of the acoustic emission signals from the friction zone of tribosystems

Based on the analysis of the works devoted to the selection of informative AE parameters for the diagnosis of tribosystems, in a theoretical way the information frequency ranges in the AE signal frame, where the maximum amplitudes values are observed, have been established. It has been theoretically and experimentally established that the information frequencies depend on the following groups of factors: the constructive; technological and operational ones. The degree of influence of the factors on the change in the frequency range is established. The operational factors (slip speed and load) change the frequency range from 106 to 584 kHz, the technological factors (roughness of the friction surfaces) change the frequency range from 118 to 618 kHz, the constructive factors (the size of the friction area of the stationary triboelement) change the frequency range from 140 to 530 kHz. It has been concluded that for the effective diagnosis of tribosystems, it is necessary to previously determine the information frequency range taking into account the factors listed above. The obtained results were confirmed experimentally with the calculation of the Fisher and Cochrane criteria, which allows one to state about the presence of a correlation between the theoretical values of the information frequencies generated by the tribosystem and the experimental values of the frequencies, where the maximum amplitudes were recorded, the correlation coefficient r = 0,88. The present analysis can be the basis for the development of a diagnostic method for tribosystems during their operation, which will increase the robustness and information content of the AE method.

New AE signals for paliperidone detected in South Korea

New AE signals for paliperidone detected in South Korea

The metal structures technical diagnostics system by acoustuc emission method control process automation models and schematic solution

The need to develop hardware for the technical diagnostics of the strength properties of metal structures is explained by the need for continuous monitoring of the state of industrial objects in the systems of technical diagnostics, which allow to record the force response to changes caused by changes in the loading conditions of the material structure. The current state of technical diagnostics equipment is considered. It is proved that the main principle of control automation in the systems of technical diagnostics of the strength properties of materials by acoustic emission methods is the detection and identification of signals, their amplification, frequency filtering, discrimination and normalization of pulses in duration and amplitude. The use of these operations allows the automated passport system to process the primary data in real time and to perform an integrated assessment of the state of the object at different stages of its life cycle. A structural diagram of the receiving equipment for measuring acoustic emission parameters, a number of designs of acoustic sensors and hardware for processing acoustic emission signals, which guarantee high quality performance of metal structures. On the basis of the analysis of modern and foreign equipment, which became widespread in the practice of technical diagnostics by the method of acoustic emission, the directions of formation of the acoustic tract of diagnostic equipment and the basic requirements for the design of the recording equipment are formulated. It is established that information support of automated systems of control and diagnostics of metal structures requires determination of their informative parameters. It is proved that the main characteristic of diagnostics of the state of metal structures in the course of their operation is the flow of AE signals, which is determined by the average value of the pulse amplitude, the dispersion of the amplitude, the amplitude distribution, the amplitude frequency distribution of time intervals between pulses. The recovery of information obtained by the diagnostic system from the AE source is the basic principle of the construction of automated control systems and diagnostics of metal structures.

Experimental investigation on rockburst process and failure characteristics in trapezoidal tunnel under different lateral stresses

In general, the in-situ stress increases with the increase of excavation depth, and it significantly affects the safe and long-term stability of tunnels and chambers. To study the influence of the in-situ stress on the rockburst process and failure characteristics, three different lateral stresses were loaded to perform biaxial compression experiments on sandstone specimens with a trapezoidal opening. The results indicate that the high lateral stress accelerates the formation of localized damage around the trapezoidal opening, which can effectively consume the elastic strain energy. The deep surrounding rock at the roof and floor are basically in a compressive stress state, and the tangential compressive stress in the deep surrounding rock of the sidewall is greater than that in the deep surrounding rock of the roof and floor, which can cause the deep surrounding rock of the sidewall to be damaged more severely. For the corners of the trapezoidal opening, the high lateral stress can restrain the rotation of the principal stress, which lead to the reduction of the crack density around the corners. AE signals and CT scanning show that the failure mode of the model specimen shifts from tensile fracture to mixed tensile and shear fracture with the increase of the lateral stress. Under different lateral stresses, the outlines of failure zones on both sidewalls of trapezoidal opening are V-shaped, and the damage degree at the sidewall of the trapezoidal opening increases with the increase of the lateral stress when the rockburst occurs. Additionally, the failure zones on both sidewalls are larger than those of circular opening, which indicate that the supporting area on the sidewall of trapezoidal opening needs to be larger than that on the sidewall of circular opening.

Monitoring of material-removal mechanism in micro-electrical discharge machining by pulse classification and acoustic emission signals

Micro-electrical discharge machining is a stochastic process where the interaction between the materials and the process parameters are difficult to understand. Monitoring of the process becomes necessary to achieve the dimensional accuracy of the micro-featured components. Although thermo-mechanical erosion is the most accepted material-removal mechanism, it fails to explain the material removal with very short pulse duration. Alternative postulate like electrostatic force-induced stress yielding provides a stronger argument, rising ambiguity over the material-removal process in the micro-electrical discharge machining regime. In this work, it was found that the stress waves released from the material during micro-electrical discharge-machining process indicate material removal by mechanical deformation and fracture mechanism. These stress waves were captured using the acoustic emission sensor. The discharge pulses were captured by voltage measurement and classified using voltage gradient and machining time duration into three major categories, open pulse, normal pulse and arc pulse. The acoustic emission signal features were extracted and identified by time–frequency–energy distribution analysis. A feed-forward back-propagation neural network mapping of the pulse instances was performed with the obtained acoustic emission signature. The time–frequency–energy distribution analysis of the acoustic emission and the scanning electron microscope images of the craters provide conclusive evidence that the material is removed by mechanical stress and fracture. The feed-forward back-propagation network model was trained to predict the discharge categories of the pulse instances with AE signal inputs which can be used for monitoring the material-removal mechanism in micro-electrical discharge machining operation.

Three-phase induction motor loading estimation based on Wavelet Transform and low-cost piezoelectric sensors

Abstract Against the backdrop of high-level industrial process monitoring, the enhancement of sensor-based solutions to increase the efficiency of predictive maintenance plans and anticipate equipment failures has been the focus of several studies. Among the industrial machinery, three-phase induction motors (TIMs) stand out as protagonists due to their operational qualities and easy acquisition. In this context, the main goal of this work is to assess the application of low-cost piezoelectric sensors to estimate the loading of a TIM by applying the Wavelet transform (WT). Therefore, this novel technique may offer a helpful control tool for TIM powered processes. The proposed approach offers the benefit of being a non-destructive technique (NDT) for industrial monitoring. In addition to the loading estimation, the results also outlined the capability of the piezoelectric sensor for AE signal analysis. Finally, this work demonstrates that the loading can modify the vibration pattern in TIMs, allowing the proposed estimation.

Failure Analysis of Polymer Blinder Using Acoustic Emission Method

In this work the features of the propagation of the acoustic waves in the matrix sample (DERAKANE 411-350 epoxy vinyl ester resin) by the source pencil lead break (PLB) with different places and extract the feature of the registered AE parameters from the tensile test were studied. Using the typical features of the AE signals such as the frequency characteristic and the energy of the signals for classify and characterize the AE source in both PLB and tensile test. By analyzing the features of the AE signals based on the continuous wavelet transform, the features of the high frequency and the energy of the signal can be used to characterize the AE source, which is useful to establish relation between the characteristics of acoustic signals and the parameter of the fracture of structure in the material.

Continuous Leak Detection and Location through the Optimal Mother Wavelet Transform to AE Signal

AbstractThis study is interested in executing an optimal wavelet transform (WT) to interpret the continuous leak acoustic emission signal precisely. Thus, this paper proposes detailed guidelines on...

Effects of carbon nanotubes on open-hole carbon fiber reinforced polymer composites

Properties and damage evolution of open-hole carbon fiber-reinforced composite laminates without/with MWCNTs during tensile damage were monitored by a complementary technology combining acoustic emission, digital image correlation and finite elements analysis. Meanwhile, the AE signals can be post-processed by fuzzy C-Means. It was concluded that adding amount of MWCNTs can reduce the stress concentration, improve the strength and fracture interface stiffness of laminate specimens and prevent the evolution of micro-cracks. The AE signals are concentrated in three areas: 23-74 kHz (matrix cracking), 82-120 kHz (fiber pull-out and delamination), 120-190 kHz (fiber breakage), respectively. An enhancement of properties of materials is obtained correspondingly due to the addition of MWCNTs into matrix. The number and amplitude of AE signals corresponding to matrix cracking produced by the specimen without MWCNTs are much larger than that of the specimen with MWCNTs, indicating that the damage degree of matrix cracking for the specimen without MWCNTs is more serious. The properties and damage evolution of composites can be studied from experimental research and numerical simulation, respectively.