Acoustic Emission Signal Energy Research Articles

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.

Energy Characterization of Short-Circuiting Transfer of Metal Droplet in Gas Metal Arc Welding

The structure-borne acoustic emission (AE) signals were detected in real time in gas metal arc (GMA) welding and pulse GMA (P-GMA) welding. According to the AE signals, the mode of short-circuiting transfer was analyzed, and the energy gradient and total energy were calculated. The calculation to the AE signals of one metal droplet transfer (MDT) showed that the energy gradient increased with increasing welding heat input not only in GMA welding but also in P-GMA welding. The energy gradient of one MDT in P-GMA welding was higher than that in GMA welding, which indicated that a high energy gradient was the basic reason for the additional vibration energy provided by pulse effect in P-GMA welding. The total energy of AE signals increased with increasing welding heat input not only in GMA welding but also in P-GMA welding. The total energy of AE signals in P-GMA welding was higher than that in GMA welding, which indicated that the additional vibration energy provided by welding pulses was the main cause of the grain structure refining in P-GMA welding. So, the results provided another means to predict the weld grain size and optimize the welding process by AE signals detected in welding.

Acoustic Emission at the Kinetic and Development of the Structural Defects under Deformation of Aluminum Alloy

The paper presents the results of studies the deformation behavior of aluminium alloy D16 by acoustic emission (AE) method. The purpose of this study was to establish the deformation stages and deformation mechanisms at each stage. Studies were carried out on the samples of aluminum alloy D16 (analog 7075). This paper contains a method for the separation of AE signals. The method of AE sources identification based on the the two-parameter distribution analysis (frequency parameter Kfvs energy of AE signals). The frequency parameter Kf is based on wavelet transform of AE signals. Two-parameter distribution allows one to separate the AE signals emitted by dislocations from the signals of micro cracks. The investigation results allowed the various deformation stages to establish by the different types of AE signals. By the AE analysis shows the dislocation mechanism of hardening the aluminum alloyD16. The paper presents the results that characterize the influences of heat treatment and structural condition of aluminum alloy on the AE parameters.

Real-time evaluation of energy attenuation: A novel approach to acoustic emission analysis for damage monitoring of ceramic matrix composites

Abstract This paper proposes a new approach to the analysis of acoustic emission data. The energy of acoustic emission signals recorded at two sensors is used to evaluate real-time energy attenuation due to damage accumulation. The method is applied to acoustic emission data recorded during static fatigue tests at intermediate temperatures on ceramic matrix composites. The evaluation of energy attenuation appears as a new indicator for damage monitoring and lifetime prediction, the attenuation increase being attributed to transverse matrix cracks opening.

Acoustic Emission Source Location Using a Distributed Feedback Fiber Laser Rosette

This paper proposes an approach for acoustic emission (AE) source localization in a large marble stone using distributed feedback (DFB) fiber lasers. The aim of this study is to detect damage in structures such as those found in civil applications. The directional sensitivity of DFB fiber laser is investigated by calculating location coefficient using a method of digital signal analysis. In this, autocorrelation is used to extract the location coefficient from the periodic AE signal and wavelet packet energy is calculated to get the location coefficient of a burst AE source. Normalization is processed to eliminate the influence of distance and intensity of AE source. Then a new location algorithm based on the location coefficient is presented and tested to determine the location of AE source using a Delta (Δ) DFB fiber laser rosette configuration. The advantage of the proposed algorithm over the traditional methods based on fiber Bragg Grating (FBG) include the capability of: having higher strain resolution for AE detection and taking into account two different types of AE source for location.

Wavelet-based acoustic emission characterization of surface damages during experimental simulation of sheet metal forming process

In this study, acoustic emission monitoring with a wavelet-based signal processing technique is developed to detect different surface damage mechanisms during experimental simulation of sheet metal forming processes. Firstly, the obtained acoustic emission signals are decomposed into various wavelet levels. Each level includes detail and approximation that are called components and related to a specific frequency range. Secondly, the energy distribution criterion is applied to find more significant components each one of which is in relation to a distinct type of damage. Results showed that the energy of acoustic emission signals was concentrated in four significant components which can be attributed to three specific dominant phenomena occurred during different stages of a well-known surface damage, i.e. galling. Indeed to compare the results with previous investigations, surface observations were used to determine how the different surface damage mechanisms are related to the dominant corresponding wavelet components.

Damage Categorization of Glass/Epoxy Composite Material Under Mode II Delamination Using Acoustic Emission Data: A Clustering Approach to Elucidate Wavelet Transformation Analysis

Delamination is the most common failure mode in composite materials, since it will result in the reduction of stiffness and can grow throughout other layers. Delamination consists of two main stages: initiation and propagation. Understanding the behavior of the material in these zones is imperative, hence the identification of this mode of failure is of great importance. There are several methods to identify damage in materials, one of which is using acoustic emission (AE) signals. Most of the pervious works have used statistical methods based on the energy of AE signals, but in this study, the normalized form of shock wave is used. The aim of this study is to extract a general pattern for specific damage from AE signals including all of the other damage signals. The method consists of a discrete wavelet packet decomposition of AE signals accompanied with a clustering algorithm, which gives the distribution of the normalized AE signal energy on the frequency band. Test set-up involved End Notched Flexure (ENF) test to detect mode II delamination on glass/epoxy composite material. The data obtained from ENF test specimens is used for the wavelet packet decomposition, and the energy of different levels of decomposition for each shock wave is clustered using different clustering algorithms including K-means and Fuzzy C-mean. Scanning Electron Microscope was used to validate the results.

ЗАКОНОМІРНОСТІ АКУСТИЧНОГО ВИПРОМІНЮВАННЯ У РАЗІ ЗРОСТАННЯ НАВАНТАЖЕННЯ НА ПАРУ ТЕРТЯ З КОМПОЗИЦІЙНОГО МАТЕРІАЛУ

Подано результати моделювання акустичного випромінювання зі зростанням осьового навантаження на пару тертя з композиційного матеріалу. Показано, що збільшення осьового навантаження приводить до зростання амплітудних та енергетичних параметрів результуючих сигналів акустичної емісії. Визначено залежності процентного приросту амплітудних та енергетичних параметрів результуючих сигналів акустичної емісії. Описано, що зі збільшенням осьового навантаження на пару тертя підвищення середнього рівня амплітуди випереджає зростання його стандартного відхилення та дисперсії. Розглянуто найбільш чутливі параметри до зростання осьового навантаження на пару тертя – дисперсія середнього рівня енергії результуючих сигналів акустичної емісії

Stable and unstable fatigue prediction for A572 structural steel using acoustic emission

The association of acoustic emission (AE) signals with crack growth behavior in the material of interest is the basis for monitoring the fatigue damage of in-service steel structures with the AE method. A model including the absolute energy rate of AE, stress intensity, fracture toughness and load ratio is presented to predict crack extension and remaining fatigue life for stable and unstable crack stages. The model is based on the Forman equation, and the balance between AE signal energy and the energy released due to crack growth. Results from AE-monitored fatigue tests with load ratios of 0.02, 0.1 and 0.7 are utilized to validate the presented model. To separate AE signals associated with crack growth from noise, a combined approach involving pattern recognition and analysis of waveform features was employed. Prediction procedures are demonstrated based on the presented model and experimental data. Reasonable agreement exists between the observed and predicted test results. The presented model conservatively estimates fatigue damage and remaining fatigue life.

Characterization of composite materials damage under quasi-static three-point bending test using wavelet and fuzzy C-means clustering

In this study, two types of specimens, woven [0, 90]s and unidirectional [0]s glass/epoxy composites, were studied. Acoustic emission (AE) monitoring with wavelet-based signal processing technique and Fuzzy C-Means (FCM) clustering method was used to detect the different fracture mechanisms during delamination in quasi-static three-point bending test. The three-point bending test simulates thrust force, the most effective factor in delamination, throughout the process of drilling without backup plate. The obtained AE signals were decomposed into various wavelet levels and classified using FCM. Scanning Electron Microscopy (SEM) observation was used to determine the different fracture mechanisms. The results show that the energy of AE signals has been concentrated in two significant components for both types of specimens, and the dependency percentage of damages in the two specimens is different.

Study of the Relationship between Concrete Fracture Energy and AE Signal Energy under Uniaxial Compression

When cracks occur in concrete, released fracture energy will be proportionally transformed into the energy contained in acoustic emission (AE). According to this physical phenomenon, AE technology provides an effective monitoring method for fracture process of concrete through acquiring generated AE. However, such monitoring is limited in qualitative evaluation of fracture process under most occasions. Quantitative interpretation of fracture process is difficult to accomplish by simply acquiring the amount of AE generated or conducting parameter-based AE analysis. This paper investigates the feasibility of reflecting the fracture energy released during fracture by means of evaluating the energy index of detected AE signals. An effective fracture model based on fracture behavior of concrete cylinder under uniaxial compression is introduced here to provide a mathematical relationship between acquired AE energy index and crack formation energy of concrete. Apart from reasonably estimating the energy consumed for crack formation, cement-based piezoelectric sensors are embedded inside the concrete to carry the task of detecting AE and transforming its energy into the electrical energy of AE signals. On the basis of experimental study, the energy of detected AE signal is satisfactorily correlated to the corresponding fracture energy and quantitatively represents the fracture energy releasing process of concrete during the period of stable cracks development. DOI: 10.1061/ (ASCE)MT.1943-5533.0000418. © 2012 American Society of Civil Engineers.

Impact Damage Detection and Assessment in Composite Panels using Macro Fibre Composites Transducers

Structural health monitoring of composite components is vital to the use of these materials in aerospace applications. Being highly susceptible to impact damage, composite materials can sustain internal damage that is very difficult to detect externally. This paper explores the use of macro fibre composite (MFC) transducers not only to detect acoustic emission (AE) released during the impact event but also as pulse/receivers to further quantify damage. To assess the dual functionality of these transducers, two were adhered to a composite panel and subjected to a number of impacts. A commercial AE system recorded signals during the impact event. After each impact, signals were pulsed and received between the two transducers and a C-scan inspection of the panel was conducted to assess the extent of the damage. Post test analysis demonstrated a clear correlation between the AE signal energy and the increase in delamination size. Furthermore, a cross correlation technique was utilised to compare signals in the undamaged plate with those at varying damage levels. The results demonstrated a decreasing correlation of signals with increasing damage severity. The results have shown that MFC transducers offer a real possibility for identifying and sizing impact damage in composite structures.

Acoustic emission in the process of liquid-phase sintering of the binary system W + 20% Cu nanopowder

The energy of acoustic emission signals in the process of sintering of powder materials is shown to be considerably lower than that obtained under plastic deformation of cast crystalline materials.

Damage Progression and Residual Strength Evaluation in Sandwich Panels Loaded at the Center

This paper addresses damage evaluation of loaded sandwich panels by using acoustic emission (AE) as a non-destructive method. The specimens were loaded monotonically out-of-plane in control of displacement and the tests were stopped at three different damage levels. Each loading level activates different failure mechanism that can influence on residual strength of material. After each quasi-static test, the damaged plate was cut by a diamond saw to obtain tensile specimens. After cutting, compression test carried out by using acoustic emission to monitor the process. Depend on loading level the damage value was variant as it caused different residual strength that was related to acoustic emission signals activities. There is a relation between AE signal energy and mechanical energy that can follow to evaluate the residual strength of panels in different loading level in sandwich panels. Results show that the using AE method having mechanical results can be effective in residual strength and progressive damage evolution.

Assessment of low-temperature embrittlement of asphalt binders using an acoustic emission approach

Thin films of paving grade asphalt binders moulded on granite substrates were stressed under rapid cooling and thermal restraint conditions at temperatures ranging from 15°C to -50°C. This temperature range encompasses typical pavement temperatures in colder climates. Differential thermal contraction between the granite substrates and asphalt binders induces progressively higher thermal stress levels in the binders as the temperature drops resulting in thermal crack formation, and the corresponding release of elastic energy in the form of transient stress waves. Using piezoelectric sensors (Digital Wave, Model B-1025), a four-channel acoustic emission (AE) system was used to record the acoustic emission activity during the binder/granite cooling process. It was observed that AE events of high energy clustered around a narrow temperature range. Assuming the cracking temperature (T CT ) to be the temperature at which the AE signal energy exceeds a pre-selected threshold energy level, this AE testing approach was found to be sensitive and repeatable for predicting cracking temperatures (T CT ) in four paving grade asphalt binders processed to two distinct ageing levels. The effect of binder type, ageing level and binder film thickness on cracking temperature is discussed. These AE-based T CT predictions showed strong correlations with predictions based on either the AASHTO TP1 or the MPIA protocols.

Wavelet-based acoustic emission characterization of damage mechanism in composite materials under mode I delamination at different interfaces

In this paper, acoustic emission (AE) monitoring with a wavelet-based signal processing technique is developed to detect the damage types during mode I delamination on glass/polyester composite materials. Two types of specimen at different midplane layups, woven/woven (T3) and unidirectional/unidirectional (T5), leading to different levels of damage evolution, were studied. Double cantilever beam (DCB) is applied to simulate delamination process for all specimens. Firstly, the obtained AE signals are decomposed into various wavelet levels. Each level includes detail and approximation that are called components and related to a specific frequency range. Secondly, the energy distribution criterion is applied to find the more significant components each one of which is in relation to a distinct type of damage. The results show that the energy of AE signals has been concentrated in three significant components for both of the specimens. There is a differ- ence in energy distribution of similar components of two specimens. It indicates that there is a dissimilar dominant damage mechanism for two different interfaces during the delamination process. Additionally, the microscopic observation (SEM) is used to determine how the different fracture mechanisms are related to the dominant corresponding wavelet components.

Acoustic emission in the fcc-fct martensitic transition ofFe68.8Pd31.2

An experimental study of acoustic emission (AE) in a single crystal and in a polycrystalline sample of ${\text{Fe}}_{68.8}{\text{Pd}}_{31.2}$ is presented. The samples are studied in a temperature range that is known to include not only a martensitic transition (MT) but also premartensitic effects and strong lattice-parameter variations below the transition. AE activity is compared to calorimetric and magnetic-susceptibility measurements. AE has only been detected during the martensitic transition. The kinetics of the MT for the single crystal exhibits a series of reproducible peaks of activity. This structured activity is not observed for the polycrystal, which shows a single-peak behavior. Despite these differences the AE measurements reveal that the martensitic transitions in both samples start at the same temperature. Results are also compatible with a negligible hysteresis at the transition. The statistics of the amplitude, energy, and duration of AE signals is analyzed in detail and characterized by power-law exponents. For the single crystal the exponents are coincident for heating and cooling ramps and are independent of the rate. For the polycrystalline sample, the exponents are different for heating and cooling.

Acoustic emissions during fracture toughness tests of steels exhibiting varying ductility

This investigation is primarily aimed at examining steels with varying ductility using characteristics of acoustic emission (AE). Four steels (AISI 1060, AISI 1080, SA333 grade 6 and AISI 304LN) were selected and their structure property relations were characterized using standard metallographic examinations, hardness and tensile properties. Fracture toughness of these steels was determined as per the guidelines of ASTM standard E1820 with simultaneous recording of AE signals. The results of these investigations have been used to demonstrate that: (a) nature of the variation of AE cumulative counts with time is different for linear and non-linear load–displacement plots, (b) synergistic analysis of the rate of change of cumulative energy, cumulative counts and intensity of AE signals provide the point of crack initiation in a material, and (c) fracture toughness of a material estimated using AE parameters is lower compared to that obtained by ASTM standard procedure.

EFFECTS OF THE MAXIMUM UNDEFORMED CHIP THICKNESS ON ROUGHNESS AND SPECIFIC ENERGY IN SURFACE GRINDING

In this study, effects of the maximum undeformed chip thickness on roughness of ground surface and specific grinding energy were investigated. The acoustic emission (AE) signals generated during grinding processes have been analyzed to find out the appropriate AE parameters for assessing the processes. SM45C steels were ground under conditions yielding volumetric removal rate per unit width of 100, 200, 300 and 400 mm3/min. From the experimental results, it is found that surface roughness ( Ra ) increases but grinding power (P), energy rate of AE signal (AErms2) and specific grinding energy(e) consumed decrease as the maximum undeformed chip thickness(g) increases.

Influence of water activity on acoustic emission of flat extruded bread

Flat extruded wheat bread and rye bread were subjected to three-point breaking test with simultaneous registration of generated vibrations. Piezoelectric sensor was used to detect vibrations and amplitude–time records were analyzed. It was found that breaking of flat extruded bread generated vibrations in whole audible spectrum. Acoustic emission signal energy expressed in arbitrary units was more dependent on water activity in low frequencies region than those in high frequencies. Transformation of amplitude–time records from time domain to frequency domain showed that regions with high level of power spectrum occurred. Dominating power spectra were in 1–3 and 7–15 kHz. It was proposed to use a ratio between those power spectra as a measure of acoustic activity of the investigated material. This descriptor was called partition power spectrum slope– β. The slope was doubled in the water activity range 0–0.5 and at higher water activities it increased sharply with increasing wetness of the material. Special software was developed to analyze amplitude–time records and detect single acoustic emission events. Majority of acoustic emission events lasted 68.1 μs, and their energy statistically was not dependent on water activity. However, number of acoustic emission events depended strongly on water activity and decreased almost 20 fold in the a w range from 0.03 to 0.75. Analysis of acoustic activity of extruded breads in both time and frequency domains suggested that it originated from simultaneous disintegration and structure microdislocations. Breaking of air cell walls caused large displacements and generated vibrations with low frequencies. Deformation of substructures, splitting of fibers, vibrations and dislocations of macromolecules in the network of the solid matrix could be responsible for generation of high frequency vibrations. It was also noted that both breads were alike when acoustic emission was analyzed in frequency domain, but they were different in the time domain. Combining both frequency and time domains showed that the breads, from the acoustic point of view, are different.