Modal Acoustic Emission Research Articles

Simulation and feature analysis of modal acoustic emission wave in planar C/SiC composite

A catastrophic accident may be caused for nearby spacecraft due to the damage occurred in C/SiC thermal protection structure. Therefore, it is significant to analyze the damage feature of the ceramic composite structure. Acoustic emission (AE) is an effective non-destructive testing method which is widely used in aerospace industry. However, some key problems should be solved when the AE technology applied to the engineering field. In this paper some propagation characteristics of AE waves in C/SiC plate were investigated based on the finite element method. Firstly, two kinds of AE sources were established by combining plate wave theory and finite element method. Secondly, a novel simulation model was established which included the mechanical characters of C/SiC composite. Then to simulate the AE source, a stepped load and a dipole force is applied to generate the release of power loss. Additionally, the results of simulation are validated through the AE experiment with the analysis method of Choi-Williams transformation. Finally, the attenuation of AE signals propagation in C/SiC plate is discussed. The results of this research work demonstrated that the simulation method of AE waves in C/SiC structure proposed in this paper can be effectively used to study the wave propagation phenomenon

Study of modal acoustic emission to monitor the impact damage in a composite plate

Based on the theory of modal acoustic emission, this paper describes a new method to determine whether a plate made of a composite material has been damaged following external impact. Using modal acoustic emission theory, the relationship between the Lamb-wave mode of acoustic emission and the force direction in the plate was analyzed. This relationship was then verified using a lead-break experiment. The Lamb-wave mode of the acoustic emission signals produced by the damage in the plate was investigated, and the criterion for assessing the impact damage was proposed. During the impact experiments, the proposed criterion was employed to monitor the impact damage of the plate. The results indicate that it is feasible to use acoustic emission signals to directly determine whether an impact had caused damage to the plate.

Modal acoustic emission for composite structures health monitoring: Issues to save computing time and algorithmic implementation

This paper deals with assessing the integrity of composite structures via modal acoustic emission (MAE) technique. It is a continuity of the paper “On the modal acoustic emission of composite structures”, published last year by the authors in the same journal. To improve the reliability level of this technique (as it is the case of the other nondestructive techniques), exploring various innovative processing techniques of the collected data is required. Unfortunately, this task undergoes a huge volume of data, where its management (processing, reuse, etc.) should be achieved as well as possible. Hence, performing an efficient processing of the large data sets that can be generated via MAE, during the composite structures health monitoring, is a challenging topic. This study concerns the development of an algorithmic tool for resolving the problem of memory saturation, which can be encountered when working with such large data sets. It is a first step towards Big Data based solutions, launched recently by the authors’ team. A case of study is discussed, showing the robustness of the already implemented algorithmic tool.

Source location using an optimized microfiber coupler sensor based on modal acoustic emission method

This paper demonstrates the application of an optimized microfiber coupler sensor (MFCS) to the source location with modal acoustic emission (MAE) method. First, based on analyzing the key influence factors of MAE method application, the package optimization of MFCS has been investigated. It is found that the best packaging length is from the groove end to the place where the 2 fibers just begin to fuse, which could achieve both, good completeness of acoustic emission signal wavelet transform and relative high sensitivity. Then, the linear source localization has been performed using the optimized MFCS. The arrival time of the acoustic emission signal is decided by the contour threshold of the wavelet transform to avoid the wave reflection from edge and mode conversion. The locating accuracy with different thresholds is analyzed. It indicates that the result agrees with the actual source position better when higher threshold is set. Furthermore, considering noise contamination and the frequency components completeness, the appropriate range of threshold is suggested to the location calculation. Finally, the favorable localization result proves that applying this optimized MFCS to the MAE source location strategy is quite feasible.

Acoustic emission source localization in thin metallic plates: A single-sensor approach based on multimodal edge reflections

This paper presents a new acoustic emission (AE) source localization for isotropic plates with reflecting boundaries. This approach that has no blind spot leverages multimodal edge reflections to identify AE sources with only a single sensor. The implementation of the proposed approach involves three main steps. First, the continuous wavelet transform (CWT) and the dispersion curves of the fundamental Lamb wave modes are utilized to estimate the distance between an AE source and a sensor. This step uses a modal acoustic emission approach. Then, an analytical model is proposed that uses the estimated distances to simulate the edge-reflected waves. Finally, the correlation between the experimental and the simulated waveforms is used to estimate the location of AE sources. Hsu-Nielsen pencil lead break (PLB) tests were performed on an aluminum plate to validate this algorithm and promising results were achieved. Based on these results, the paper reports the statistics of the localization errors.

On the modal acoustic emission testing of composite structure

This paper concerns the use of Modal Acoustic Emission (MAE) on composite overwrapped pressure vessels (COPV). It investigates the physics of this approach, defined as a promising method that can provide further information to classical acoustic emission technique. The investigations are achieved on a small coupon and full scale specimens extracted from a COPV. The separation mode was previously performed using Pencil Lead Breaks (PLBs) based on Continuous Wavelet Transform (CWT) analysis. It has been shown that extensional (S0) and flexural (A0) modes were successfully splitted and their frequency bandwidths are defined. After that, an appropriate algorithm was developed based on CWT analysis of the extracted AE signals coming from the region of damage. Results obtained by this method show a good agreement regarding the nature of damage and predominant mode expected during tensile test.

The identification of damage types in carbon fiber–reinforced plastic cross-ply laminates using a novel fiber-optic acoustic emission sensor

In this study, a phase-shifted fiber Bragg grating sensor was employed for acoustic emission detection in cross-ply carbon fiber–reinforced plastic laminates. First, we evaluated the response of the phase-shifted fiber Bragg grating sensor to a simulated acoustic emission source using a pencil lead breakage test. The existing modes of Lamb waves were observed, and their relations to the acoustic emission source orientation were investigated using a modal acoustic emission method for discriminating between acoustic emission signals generated by transverse cracking and delamination. As a result, those two types of damage were identified during a tensile test. In the time–frequency analysis of the waveforms detected by the phase-shifted fiber Bragg grating sensor, in addition to the S0 and A0 modes that are usually used in modal acoustic emissions, we found an A1 mode in the high-frequency range of the acoustic emission generated by a transverse crack. Then, we conducted a finite element analysis to examine the inherent mechanism of the A1 mode excitation. The results of the calculation almost agreed with the experimental results and indicated that a phase-shifted fiber Bragg grating sensor has a high sensitivity response to acoustic emission in the carbon fiber–reinforced plastic laminates over a broad bandwidth. Therefore, this novel fiber-optic sensor has been shown to have high potential for monitoring the ultrasonic structural health of composites.

Effect of fiber content on single tow SiC minicomposite mechanical and damage properties using acoustic emission

Ceramic matrix composites (CMCs) are attractive materials for use in temperature-critical aerospace and nuclear applications. Relating the mechanical behavior and damage mechanisms of simple ceramic matrix minicomposites to health-monitoring techniques helps to understand the fundamentals of the mechanical response of CMCs. In this study, single-tow minicomposites with a silicon carbide (SiC) matrix deposited by chemical vapor infiltration, a boron nitride or a carbon interphase, and various types of SiC fibers were tested in tension at room temperature. Modal acoustic emission (AE) was used to determine the dependence of matrix cracking on the applied load. Crack density evolution was obtained using two AE-based methods: the established method using cumulative energy of AE events and a new technique based on speed of sound measurements.

Modal acoustic emission of damage accumulation in C/C–SiC composites with different fiber architectures

The stress-dependent material behavior of carbon fiber reinforced ceramic matrix composites (C/C–SiC) was investigated with modal acoustic emission (AE) technique. AE observation is a promising health monitoring method which provides accurate location and identification of the recorded damage-related AE events. For a better understanding and identification of different damage mechanisms C/C–SiC composites with different fiber orientations were studied. Load/unload/reload tensile tests were performed and measurements were made over the entire stress range in order to determine the stress-dependence of acoustic activity for increasing damage states. In general it was found that in C/C–SiC composites a significant damage-related increase in AE energy was observed close to the ultimate tensile stress. Also, fiber architecture dependent differences during damage accumulation in terms of total number of AE events and their typical AE energy could be determined and correlated to different damage mechanisms.

Transverse cracking in carbon fiber reinforced polymer composites: Modal acoustic emission and peak frequency analysis

Abstract The initiation and propagation of cracks in carbon-fiber reinforced toughened epoxy polymer composite laminates were studied using modal acoustic emission and waveform energies, coupled with peak frequency data and correlated to matrix crack density in the transverse direction. Composites of four different ply layups were studied. Results show the placement of the 90° ply (e.g., on the surface or internal) as well as the number of adjacent 90° plies directly influence the applied stress load at which transverse cracks are formed and the resulting stress distribution. Results for matrix cracking show that peak frequency data alone was unable to fully characterize the damage initiation, contrary to prior studies. However, based on modal acoustic emission principles, coupling the peak frequency data with acoustic energy of waveforms, effectively corresponded to the stress-dependent number of 90° ply transverse cracks and the through-the-thickness location of the 90° ply. This information can be very useful to understand stress-dependent transverse cracking in a given 90° ply or to develop optimal lay-up sequences to maximize composite properties.

The Application of Finite Element Simulation on Sheet Plate Modal Acoustic Emission Testing

Based on mode acoustic emission theory, the paper uses dynamic finite element software ANSYS / LS-DYNA to simulate modal acoustic emission test, and obtains the Lamb wave propagation analog signal on sheet plate; By analyzing the analog signal, it determines the signal frequency and the Lamb wave arrival time of signal receiving point, then determines the guide wave group velocity at this frequency, and uses the method of time difference analysis to determine the dispersion curve. Comparing the simulation dispersion curve with the theoretical curve, the study has shown both curves are consistent and it is feasible to simulate modal acoustic emission signals with the finite element.

The impact of solid–fluid interaction on transient stress wave propagation due to Acoustic Emissions in multi-layer plate structures

In this work the effect of a solid–fluid interaction on stress wave propagation within a composite overwrapped pressure vessel (COPV) was investigated. A modeling approach capable of adequately capturing the multi-physics nature of the solid–fluid interaction is presented, and then validated through comparison to experimental waveforms and time–frequency distributions. With a validated modeling approach, a numerical study on stress wave propagation in COPV structures was undertaken. It was found that the compressibility of the pressurizing media used during the pressure testing of COPVs has an effect on the leakage of the propagating Lamb modes, as well as alternative direct paths that may propagate within the fluid. Results regarding the effects of the most common microstructural deformation mechanisms that occur in composite materials on the detected Lamb modes, as well as on the direct fluid path arrival are presented. Finally, the impact of source depth on the detected Lamb modes and the direct fluid path arrival was investigated. It was found that information gleaned from the direct fluid path arrival may have the potential for aiding Modal Acoustic Emission practices in source mechanism identification, determination of source orientation, as well as source depth estimation.

Modal Acoustic Emission Investigation for Progressive Failure Monitoring in Thin Composite Plates under Tensile Test

Acoustic Emission (AE) is one of the popular non-destructive (NDT) techniques and its applications have increased subsequently for Structural Health Monitoring (SHM). During the past few decades, many successful research works have evidently shown remarkable capability of AE for early damage detection of composite materials. This paper investigated the application of single channel acoustic emission (AE) source location detection method, utilizing time-frequency analysis for thin composite plates. Besides, failure characterization using Modal Acoustic Emission (MAE) also presented. Modal analysis of AE signals or MAE can offers a better theoretical background for acoustic emission analysis; which is necessary to get more qualitative and quantitative result and therefore, increase the reliability of early failure characterization for thin composite plates. For this study, tensile tests were conducted on the glass fiber epoxy resin specimen with small notch; and four channels of acoustic emission system were used to acquire AE signals. The results revealed that in practical, single channel AE source location was difficult to be done. Also, the study has successfully showed that matrix cracks and fiber fracture produced AE signals which dominated by symmetric wave mode.

The Corrosion Acoustic Emission Source Location Technique and its New Trend

The corrosion acoustic emission (AE) source location is one of the main purposes of acoustic emission testing (AET), corrosion detection and location can guarantee the safety and integrity of pipeline, storage tank and other equipment in the petrochemical industry. The computed source location and zonal location methods are reviewed in this paper, and also new source location method based on modal acoustic emission (MAE) is introduced and this new method will be more widely used in the field of corrosion detection in future.

A modal acoustic emission signal classification scheme derived from finite element simulation

The ability of broadband modal acoustic emission to classify the most common forms of damage mechanisms occurring within a polymer matrix composite material with rod type geometry has been shown. The composite under study was a unidirectional hybrid polymer matrix composite material, with carbon and glass fibers reinforcing a high temperature epoxy matrix. Signal discrimination was achieved through the development of a classification scheme derived from explicit finite element simulation of the most common deformation mechanisms. The classification scheme identified the type of failure mechanism, as well as the material of origin, based upon the spectral content of the signal which is directly influenced by the wave modes that propagate. The classification scheme was used to evaluate the effect that atmospheric aging at elevated temperature had on the hybrid composite subjected to flexure loading at various time periods. Advantages of the proposed method include computational efficiency, the ability to inherently account for geometric and material boundary layer reflections, as well as the ability to be readily adapted to complex part geometries.

Acoustic emission monitoring of composite containment systems

This paper considers two different types of composite containment system, and two different types of acoustic emission (AE) monitoring approach. The first system is a composite reinforced pressure vessel (CRPV) which is monitored both during construction and in-service using a broadband modal acoustic emission (MAE) technique. The second system is a membrane cargo containment system which is monitored using both a global as well as a local AE technique. For the CRPV, the damage assessment is concerned mainly with the integrity of the composite outer layer at the construction stage, and possible fatigue cracking of the inner steel liner at the in-service stage. For the membrane tank, the damage assessment is concerned with locating and quantifying any abnormal porosities that might develop in-service. By comparing and contrasting the different types of structural system and different monitoring approaches inferences are drawn as to what role AE monitoring could take in the damage assessment of other types of composite containment system. (Detailed technical data have not been included, due to client confidentiality constraints.)

Rub-impact Acoustic Emission Signal Recognition of Rotating Machinery Based on Gaussian Mixture Model

On the basis of modal acoustic emission and narrow-band signal theory, the mathematical expression of multi-modal AE signal is given. A mixed parameter composed of logarithm cepstral coefficients and fractal dimension is presented as the characteristic coefficients of rub-impact AE signal, and the AE recognition system based on Gaussian mixture model is also established. Because the eigenvector of each modal wave in rub-impact AE signal is different, so a model of probability density function of eigenvector is built and it is regarded as a clustering. Training model is established with mean, covariance matrix and probability of each clustering. Sum likelihood probability weighted by maximal ratio combining to likelihood probability of Gaussian model will be obtained when the tested signal is recognized, if the probability is larger than a set threshold, it can be confirmed that rub-impact AE is available. Rub impact AE signals are sampled from rotor test stand, the types of input model of Gaussian are sorted by AE wavrform shapes and its fractal dimensions, then white noise and non-stationary noise are added to simulate the real AE signal. In the end, this Gaussian mixture model is used for AE recognition. The results indicate that the model has high recognition rate and good anti-noise ability.

Modal Analysis of Rubbing Acoustic Emission for Rotor-Bearing System Based on Reassigned Wavelet Scalogram

Rubbing between the rotor and the stator is the frequent and harmful malfunction in the rotating machinery, which will cause a very serious accident, even catastrophe, to the machine. Thus, such fault needs timely detection to avoid severe consequences. Vibration based methods are the traditional ones for the detection and diagnosis of the rubbing fault, which are effective when the rubbing has been severe, but always do not work in early detection of such fault. Rubbing between the rotor and the stator will cause elastic strain in the rubbing location and thus can produce acoustic emission (AE). Apparently, such AE contains direct and abundant information about the rubbing and thus can be used to detect and diagnose such fault effectively. In this paper, the AE based method is proposed for detecting and identifying the rubbing of the rotor-bearing system. Using the modal acoustic emission (MAE) theory and reassigned wavelet scalogram, the present study emphasizes on modal analysis and time-frequency characteristics analysis for further understanding the characteristics, phenomenon, and features of the rubbing AE. The results show that the rubbing AE is the elastic wave with multiple modals, which has an impact characteristic and mainly consists of the flexural wave and extensional wave. The transmission of the rubbing AE has some directivity. Moreover, different modals have different transmission characteristics: The flexural wave has lower frequency and its attenuation is influenced mainly by the sectional area of the transmission passage. The extensional wave has higher frequency and its attenuation is mainly sensitive to the interface transmission between the two surfaces. The results also reveal that the reassigned wavelet scalogram is more effective than its original scalogram for the characteristic analysis of the rubbing AE.

Acoustic emission source location methods using mode and frequency analysis

Traditional acoustic source location techniques are greatly affected by the threshold value of the acoustic signals. Based on the theory of modal acoustic emission, acoustic signals have characteristics indicative of multi-mode, broad band and dispersion. One-dimensional acoustic source location theory is developed to incorporate these characteristics. The arrival times and wave velocities needed for source location are influenced by mode and frequency. Based on the number of sensors used, two universal source location techniques have been investigated. To obtain the arrival time of one mode at certain frequency, the Gabor wavelet transform is applied to the analysis of acoustic signals. One-dimensional acoustic source location experiments in a thin plate have been performed using a lead break as acoustic source. The acoustic source location techniques have been greatly improved and the accuracy of these acoustic source location methods has been verified. Copyright © 2007 John Wiley & Sons, Ltd.

Acoustic emission characteristics of rub-impact for rotor-bearing system based on wavelet scalogram

Rub-impact between the rotor and the stator in the rotor-bearing system will cause elastic strain in the rubbing location and thus can produce acoustic emission. Therefore, such acoustic emission can be used to identify and diagnose the rub-impact fault. Analyzing the acoustic emission characteris-tics of the rub-impact in the rotor-bearing system is emphasized by the experiment. At first, in light rub-impact situation, the acoustic emission and the vibration signal are compared and analyzed to demonstrate the superiority of the acoustic emission based method for the rub-impact identification. Then, the wavelet scalogram is introduced in detail and its characteristics are illustrated through simulation. Finally, the specific experi-ments are performed. And the wavelet scalogram is used to analyze and discuss the time-frequency features, propagation characteristic and frequency dispersion characteristic of the rub-impact acoustic emission. The results reveal that the rub-impact acoustic emission is the multi-modal elastic wave which mainly includes the flexural wave and extensional wave. It is also indicated that the wavelet scalogram is the strong analysis method for the wave analysis of the modal acoustic emission.