Acoustic Emission Signal Energy Research Articles

Temperature aging effects on mechanical behavior of structural GFRP on interlaminar shear tests

Aging of polymer composites is a wide-spread problem, which causes deterioration of mechanical properties, shorter design service life of structures and their potential early destruction. The work presents the results of experimental researches, within which the impact of elevated temperatures on mechanical properties of airborne constructional fiberglass were investigated. Research results were obtained, which describe the impact of the preliminary temperature aging (in different modes) on mechanical properties, behavior and execution of different composite destruction mechanisms during interlaminar shear testing. Experimental data were obtained, which describe the temperature impact on the mechanical behavior of constructional fiberglass samples at interlaminar shear. Regularities of fiberglass properties changing after temperature aging at interlaminar shear were analyzed, based on the joint use of testing systems and an acoustic emission (AE) signals recording system. Dependences of AE signal energy parameters on the time, combined with diagrams of fiberglass samples loading were obtained. Results of the distribution of specific frequency bands obtained after the destruction of samples with different preliminary aging modes, are graphically represented.

Acoustic-Emission Procedure for Rejecting Defects in Multiple-Pass Girth Welds

A procedure is proposed for rejecting girth welds based on an analysis of the main parameters of acoustic emission (AE) signals recorded during multiple-pass welding. The accuracy of locating AE signals recorded from defects and their filtering from noise and interference were ensured by the use of a modified tabular method and rejection grid. Normalized coefficients were calculated from the energy and amplitude of localized AE signals and used for in-process assessment of weld quality. Threshold values were determined for the normalized coefficients above which the weld is rejected. Defects in girth welds were identified using this procedure, and the possibility of determining defect hazardousness in real time was demonstrated.

Effect of moisture content on propagation characteristics of acoustic emission signal of Pinus massoniana Lamb

The propagation velocity and energy of acoustic emission (AE) signals at different moisture contents (MC) of wood are studied, providing a theoretical basis for studying the law of wood stress and strain with the change in MC. The AE source was simulated by lead core fracture on the surface of Pinus massoniana Lamb. Signal de-noising was performed by discrete wavelet decomposition method. On this basis, the propagation velocity and energy of AE signals at different MCs were studied according to the signal cross-correlation analysis and time difference localization method, and the law of velocity and energy change with MC was further determined by fitting. The fitting results show that the propagation velocity of AE signals decreased exponentially with the increase in MC. Moreover, the propagation velocity decreased rapidly when the MC was below fiber saturation point (FSP), and decreased relatively gently when the MC was above FSP. In addition, the energy attenuation of the AE signal was obvious during the propagation process, and the energy attenuation rate of the AE signal presented a linear relationship with the increase in MC. The change in MC has a significant effect on the propagation velocity and energy of AE signals of wood.

Experimental Results of Acoustic Emission Attenuation Due toWave Propagation in Composites

Recently, acoustic emission-based damage classification schemes gained attention for health monitoring of composites. Here, the reliable detection of different micro-mechanical damage mechanisms is important because of the adverse effect on fatigue life. It is well known that classical parameters obtained from acoustic emission measurements in time domain are strongly dependent on the propagation path and testing conditions. However, signal attenuation, which can be observed due to geometric spreading, material-related damping, and dispersion, is typically neglected. Therefore, it is generally assumed that frequency domain features are reliable descriptors of damage due to invariance of peak frequencies to the propagation path. Based on this assumption, several data-driven approaches for damage detection are developed. However, in contrast to metallic materials, where low attenuation is observed, acoustic emission signals are strongly attenuated in polymer matrix composites due to viscoelastic behavior of the matrix. For instance, it is reported in literature that at high frequencies most of the acoustic emission signal energy is attenuated after a propagation distance of 250~mm. Therefore, new experimental results of acoustic emission attenuation in composites are presented in this paper. Particular focus is placed on the frequency dependence of acoustic emission attenuation and the effect of different loading conditions. The specimens are manufactured from aerospace material. Carbon fiber reinforced polymer plates are used as a typical specimen geometry. Different acoustic emission sources are considered and the related attenuation coefficients are determined. Furthermore, full waveform data are analyzed in time and time-frequency domain using wavelet transform. From the experimental results it can be concluded that consideration of wave propagation-related signal attenuation is important for the interpretation of acoustic emission measurements for health monitoring of composites. Consequently, the impact on the detectability of different physical damage mechanisms using data-driven classification approaches has to be considered.

Health monitoring of reinforced concrete structures with hysteretic dampers subjected to dynamical loads by means of the acoustic emission energy

A test specimen representing a scaled reinforced concrete frame structure with hysteretic dampers was subjected to sequential seismic simulations of incremental peak acceleration on a 3 × 3 m2 shaking table. From this specimen, two beam–column connections—one exterior and one interior—were continuously monitored with wideband low-frequency acoustic emission sensors properly attached on the structure. Complementing other Non-Destructive Testing (NDT) methods, acoustic emission has proven to be a reliable technology for structural health monitoring within a predictive maintenance program. In particular, it was found that the accumulated energy of acoustic emission signals—properly filtered by means of the root mean squared and the spectral partial power of the waveforms in order to avoid the influence of secondary sources—correlated well with the plastic strain energy released by the specimen. Moreover, the use of the rise angle and average frequency of the filtered acoustic emission signals allowed for successful discernment between tensile and shear cracks in the concrete. The acoustic emission energy associated with shear cracks was found to be substantially lesser than that corresponding to tensile crack. This observation is consistent with the fact that the beams and column of the tested reinforced concrete frame were designed under modern codes aimed at preventing the brittle shear failure of members.

Statistical Regularities of Formation of a Main Crack in a Structurally Inhomogeneous Material under Various Deformation Conditions

The peculiarities of the formation of a main crack in the Westerly granite samples under quasistatic uniaxial compression without any lateral upthrust have been studied using the data of acoustic emission (AE) and X-ray computer microtomography (CT). The multifractal analysis of pauses between acoustic emission events and the analysis of the energy distribution functional forms of the AE signal have been performed. According to the computer tomography data, defects form only near a future main crack; i.e., no stage of disperse accumulation of defects over entire sample volume has been revealed. Two stages of the main crack formation have been observed: the first stage is characterized by an exponential energy distribution of AE signals and the second stage is characterized by a power low of the AE signal energy distribution. The multifractal analysis of the pauses between neighboring AE signals demonstrate the transition from the multifractal dynamics of the acoustic emission to the monofractal dynamics when approaching a fracture moment.

Acoustic emission analysis for tool wear state during friction stir joining of SiCp/Al composite

As a key component of friction stir joining (FSJ), tools play an important role in welding quality and welding performance. In this study, the acoustic emission (AE) signal acquisition system was established. The AE signals from FSJ of SiCp/Al composites were analyzed in the time domain, frequency domain, and time-frequency domain respectively. The root mean square (RMS) value, spectrum distribution, and energy distribution of AE signals during FSJ were obtained. The relationship between the tool wear state and the AE signal was studied. The results show that with the increase of welding times, the wear degree of the pin is aggravating. The more serious the tool was worn, the greater the RMS value of the acoustic emission signal was. With the increase of wear, the energy of AE signals gradually moves to the low-frequency region, and the spectrum tends to be concentrated. According to wavelet packet decomposition of AE signals, it has been found that in the frequency bands 3–8, the energy percentage increases with the aggravation of agitation tool wear, while the opposite trend appears in the frequency bands 10–16.

Acoustic emission characterization of sliding wear under condition of direct and inverse transformations in low-temperature degradation aged Y-TZP and Y-TZP-AL2O3

In this research, results of the investigation of the sliding friction and wear of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) and Y-TZP-Al2O3 samples preliminarily subjected to low-temperature degradation are reported. The investigation was carried out using a pin-on-disk tribometer with simultaneous recording of acoustic emission (AE) and vibration acceleration. The sliding wear process was found to be determined by dynamic direct and inverse Y-TZP transformations detected by monoclinic and tetragonal X-ray diffraction peak ratios. The AE signals generated under direct and inverse transformations can be used to characterize wear and friction mechanisms as well as direct and inversed sliding-induced phase transformations. The AE signal energy grows with the friction coefficient and the inverse transformation degree. Reduction of the AE signal energy indicates establishing the mild wear stage caused by effective stress-induced direct martensitic transformation. The AE signal median frequency increases in the case of lower friction. Numerical studies of wear subsurface fracture under conditions of stress-induced martensitic transformation were used to elucidate the role played by the phase transformation in Y-TZP and Y-TZP-Al2O3. Martensitic transformation in Y-TZP was described with use of the non-associated dilatant plasticity model. Simulation results particularly show that increase in the value of dilatancy coefficient from 0 to 0.2 is accompanied by 25%−30% reduce in characteristic length and penetration depth of sliding-induced subsurface cracks. As shown the AE may be an effective tool for in-situ monitoring the subsurface wear of materials experiencing both direct and inverse transformations.

Continuous monitoring of tightening condition of single-lap bolted composite joints using intrinsic mode functions of acoustic emission signals: a proof-of-concept study

Intrinsic mode functions of acoustic emission signals, extracted from signals using empirical mode decomposition, were used to characterize the contact conditions of asperities (e.g. sliding friction or collision) in the mating parts of bolted composite joints undergone flexural vibration, whereby to evaluate the tightening condition of the joints quantitatively. Specifically, the sliding friction–related intrinsic mode functions, generated in the mating parts of the two joining composite components (termed as C-C contact), were ascertained from those generated from the contacts between the joining components and metallic fasteners (termed as M-C contact), via a Hilbert–Huang transform. Subsequently, the C-C contact–related intrinsic mode functions were linked to the contact behaviors of asperities at the joining interfaces, reflecting quantitatively the degree of the residual torque of the bolted joints. The fatigue performance of the joints was further evaluated according to the changes in the energy ratios of the C-C contact–related intrinsic mode functions. Experimental results have revealed that the gross energy of acoustic emission signals is capable of evaluating the residual torque of the joints within a limited range. Vibration loosening of composite joints was found to result in an increase in the energy ratios of C-C contact–related high-frequency intrinsic mode functions, on which basis the detectability of the acoustic emission–based structural health monitoring is further improved, making it possible to evaluate the tightening condition of a bolted joint when the joint undergoes vibration fatigue. This proof-of-concept study provides a promising solution to evaluate the contact conditions of bolted composite joints during assembly and to continuously monitor the tightening condition throughout the service life of the joints using the acoustic emission technique.

Failure mechanism of glass-fiber reinforced laminates influenced by the copper film in three-point bending

In this paper the influence of copper film on the stress distribution, damage evolution and failure mechanism of glass-fiber reinforced laminates was investigated. The specimens were tested at the in situ three-point bending tester. Simultaneously, a microscope and acoustic emission (AE) system were applied to in situ characterize the damage evolution of surface and inside of specimens, respectively. Moreover, a finite element analysis (FEA) model was constructed to simulate the stress distribution on the different types of specimens during the three-point bending. The result of the finite element simulation was in agreement with that of the experiment. The bending stress distribution on the specimen of glass-fiber reinforced laminates (no copper film) and double-sided copper-clad laminates was different from that of the single-sided copper-clad laminates, which made the failure mechanism of single-sided copper-clad laminates was not the same as the glass-fiber reinforced laminates and double-sided copper-clad laminates. It is obviously that the copper film can effectively improve the mechanical properties of glass-fiber reinforced laminates. The in situ images revealed the damage evolution of glass-fiber reinforced laminates and single-sided and double-sided copper-clad laminates was not the same. Furthermore, the glass-fiber fracture, the glass-fiber stripping from the substrate and matrix cracking were characterized by the amplitude, count, rise time, duration time, energy of AE signals during the three-point bending.

The study of a fatigue crack propagation in titanium Grade 2 using analysis of energy dissipation and acoustic emission data

The paper is devoted to the experimental investigation of crack propagation in metal (titanium Grade 2 alloy) under fatigue loading (cyclic uniaxial tension-compression test). To investigate the crack propagation under fatigue loading the original experimental setup was developed, which includes an acoustic emission sensor, infrared camera, contact heat flux gauge and the system for crack length monitoring. Based on the obtained experimental data the correlation between the energy dissipation caused by plastic deformation at the fatigue crack tip and the energy of acoustic emission signals was found. The analysis of contact heat flux gauge data showed two different stages energy dissipation under fatigue crack propagation. A cluster analysis of acoustic signal confirmed the existence of different regimes of acoustic activity, probably corresponded to the different fracture mechanisms under fatigue crack propagation.

Статистические закономерности формирования магистральной трещины в структурно-неоднородном материале при различных условиях деформирования

AbstractThe peculiarities of the formation of a main crack in the Westerly granite samples under quasistatic uniaxial compression without any lateral upthrust have been studied using the data of acoustic emission (AE) and X-ray computer microtomography (CT). The multifractal analysis of pauses between acoustic emission events and the analysis of the energy distribution functional forms of the AE signal have been performed. According to the computer tomography data, defects form only near a future main crack; i.e., no stage of disperse accumulation of defects over entire sample volume has been revealed. Two stages of the main crack formation have been observed: the first stage is characterized by an exponential energy distribution of AE signals and the second stage is characterized by a power low of the AE signal energy distribution. The multifractal analysis of the pauses between neighboring AE signals demonstrate the transition from the multifractal dynamics of the acoustic emission to the monofractal dynamics when approaching a fracture moment.

Study of EMR and AE during Coal Fracture under Quasi-static Uniaxial Compression Load

A quasi-static uniaxial compression experiment was designed to simulate creep damage in coal. During the experiment, electromagnetic radiation (EMR) and acoustic emission (AE) signals were synchronously acquired. The energy of EMR and AE signals were subsequently calculated after the background noise from the equipment and the environment were filtered out. We then analyzed the change in signal energy associated with the sample strength, loading time and other factors. The results showed that as the loading time increases, the frequency of the periodic signal in the EMR energy also increases. In addition, the dominant AE signal energy release occurs only in the final stage of sample failure. However, intermittent AE pulse clusters were recorded during the entire loading cycle. The analysis of data provided a strong correlation between the change in the AE signal energy and the expansion of micro-cracks in the materials, which is manifested as an irreversible deformation of the material at the macroscopic scale.

Dry sliding of Hadfield steel single crystal oriented to deformation by slip and twinning: Deformation, wear, and acoustic emission characterization

Abstract This paper studies Hadfield steel single crystals with the orientation of the normal load axis [ 1 1 8 ¯ ] and friction axis [ 4 4 1 ] . The chosen orientation implies that deformation develops by slip and twinning. Analysis of the crystallographic orientation and acting stresses has revealed stages of shear deformation development in slip systems. Consecutive tests of the same duration were conducted to study the evolution of the deformation relief. Using the fast Fourier transform, the median frequency and energy of acoustic emission signals generated at different stages of friction are analyzed. A correlation is established between changes in the acoustic emission parameters and wear of single crystals.

Investigation and identification of fracture types of structural materials by means of acoustic emission analysis

Acoustic emission (AE) signals obtained from static loading tests on different structural materials were processed by wavelet transform (WT) technique. Wavelet analysis is used to determine new relevant descriptors in order to improve the characterization and the identification of the fracture type: plastic deformation and crack initiation/growth. A correlation between the features of the continuous wavelet transform of AE signal (frequency peak, bandwidth, pulsewidth and energy) and fracture modes is presented.

Failure prediction and reliability analysis of ferrocement composite structures by incorporating machine learning into acoustic emission monitoring technique

This paper introduces suitable features and methods to define hazard rate function by acoustic emission (AE) parametric analysis to develop robust damage statement index and reliability analysis. AE signal energy was first examined to find out the relation between damage progress and AE signal energy so that a damage index based on AE signal energy could be proposed to quantify progressive damage imposed to ferrocement composite slabs. Moreover, by using AE signal strength, historic index could be computed and utilized to develop a modified hazard rate function through integration of bathtub curve and Weibull function. Furthermore, to provide a practical scheme for real condition monitoring, support vector regression was utilized to produce a robust tools for failure prediction considering uncertainties exist in real structures.

A probabilistic neural network applied in monitoring tool wear in the end milling operation via acoustic emission and cutting power signals

ABSTRACTTool condition monitoring, which is very important in machining, has improved over the past 20 years. Several process variables that are active in the cutting region, such as cutting forces, vibrations, acoustic emission (AE), noise, temperature, and surface finish, are influenced by the state of the cutting tool and the conditions of the material removal process. However, controlling these process variables to ensure adequate responses, particularly on an individual basis, is a highly complex task. The combination of AE and cutting power signals serves to indicate the improved response. In this study, a new parameter based on AE signal energy (frequency range between 100 and 300 kHz) was introduced to improve response. Tool wear in end milling was measured in each step, based on cutting power and AE signals. The wear conditions were then classified as good or bad, the signal parameters were extracted, and the probabilistic neural network was applied. The mean and skewness of cutting power and the root mean square of the power spectral density of AE showed sensitivity and were applied with about 91% accuracy. The combination of cutting power and AE with the signal energy parameter can definitely be applied in a tool wear-monitoring system.

SIMULATION OF LEGITIMACIES ACOUSTIC RADIATION ENERGY CHANGE FOR THE CONTROL OF COMPOSITE MACHINING PROCESS

Regularities of acoustic emission energy parameters change during of composite materialsmachining speed increase for the prevailing mechanical destruction its surface layer is observed. Descriptionof the obtained regularities is carried out. It is shown that during composite materials machiningspeed increase a percentage growth of acoustic emission signal energy average level dispersion outstripsa percentage growth of energy average level and its standard deviation

Study on the transient impact energy of metal droplet transfer in P-MIG welding based on acoustic emission signals analysis

According to the structure-borne acoustic emission (AE) signals detected in pulsed metal inert gas (P-MIG) welding on aluminum alloy, the energy gradient and total energy of AE signals were used to describe the rate of impact energy and total impact energy coming from metal droplet transferred into molten pool. The results showed that there were three types of energy gradient curves according to three modes of metal droplet transfer (MDT). The characteristics of energy gradient curves had a close relation to the transient impact energy of MDT. The energy gradient of MDT decreased with the rise of pulse frequency during the impact process of not only one metal droplet but also several metal droplets within 0.04s. So, the variation rate of impact energy was lowered with the raise of transfer frequency on the premise of one droplet per pulse mode. Total energy of AE signals coming from not only one metal droplet but also several metal droplets within 0.04s also demonstrated a downward trend. On the premise of one droplet per pulse mode, the variation of the transient impact energy accorded with an exponential attenuation model.

Acoustic and Emission Control of the Hereditable Stress and Strain State of the Metal Surface Layer during Cutting and Surface Plastic Deformation

Methods and experimental findings shown describe how mechanical parameters of the surface layer behavior and acoustic emission signals are interconnected.Experimental study was carried out under conditions of simple single-and dual stage compression. Graphic and analytic dependencies between the counting rate of the acoustic emission Ṅ and the shear deformation degree Λ were revealed. The findings describing dual compression show that the acoustic emission method is sensitive to the material stressing history.The dependency of the acoustic emission signal energy on the pre-stressing program was found, which helped establish that, with values of the plasticity reserve depletion being equal for all experimental specimens, the accumulated shear deformation degree Λ was different.The findings describing the hereditable physical state of the strengthened surface layer of parts during cutting and surface plastic deformation are presented in the paper. The study was carried out using the methods of property accumulation control in deformation sites depending on treatment modes with real-time monitoring of acoustic emission signals. A peculiar feature of these methods is the use of visual recording of the metal plastic flow to be further used in calculating the hereditable parameters of the surface layer quality.