Acoustic Emission Detection Research Articles

Acoustic Emission Damage Detection during Three-Point Bend Testing of Short Glass Fiber Reinforced Composite Panels: Integrity Assessment

In this study, an acoustic emission (AE) technique was used as a passive non-destructive tool to detect the damage progress in short glass fiber-reinforced composite panels. AE detection was conducted during three-point bend tests, thus illustrating the flexural damage accumulation for composite panels with different sizes and fiber volume content. To demonstrate the universality of the employed integrity assessment methodology, AE data was detected using different timing parameters and two different transducer types, i.e., medium-band and wide-band frequency sensors. The AE waveform classification presented in this study is based on peak frequency distributions. Frequency bands that are associated with certain failure mechanisms, including matrix micro-cracking, fiber debonding, delamination, and fiber breakage, were obtained from the technical literature. Through this investigation, the concept of cumulative signal strength (CSS) and cumulative rise time versus peak amplitude ratio (CRA) as AE output parameters are shown to facilitate integrity assessment for the employed complex composite material system. Significant jumps in CSS and CRA curves could be correlated to critical strain levels and distinct damage events in the composite panels subjected to flexural loading.

An Efficient Method for Wheel-Flattened Defects Detection Based on Acoustic Emission Technique.

Recent research studies show that acoustic emission (AE) technologies have great potential in detecting the flattened defects of wheel; however, the wheel-rail rolling interference (WRRI) significantly influences the accuracy of wheel defect detection. Aiming to solve the above-mentioned problem, a novel detection method, which combines an improved synthesized health index (ISHI) with a time adaptive threshold (time-ATH), is proposed in this article. In order to obtain the defect information from the signals generated by the wheels, a completed feature set that contains many types of features is extracted from AE signals. Then, the ISHI is fused by several effective features that are selected from the completed feature set, according to detection rate and accuracy. Besides, a time-ATH calculation is proposed to detect the defective signals of wheels and reduce the influence of the WRRI. The method is fully verified in actual datasets, and the results show that the proposed method achieves a better detection rate and accuracy. Moreover, it provides an effective way for the AE detection of wheel-flattened defects under strong and numerous WRRI.

Characteristics of acoustic signals emitted during millisecond laser-BK7 glass interaction

A microphone was used to study the characteristics of acoustic emission for millisecond laser-induced damage of BK7 glass. Different temporal and spectral distributions were obtained for the front and rear surface damage processes. The front surface damage was associated with the strong thermal melting process, and the size of the conical molten pit was strongly linked to the intense oscillating period of the acoustic signal. The effects of the detection distance and angle on the spectrum below 5 kHz, which were induced during the front surface damage process, were found to be associated with the distribution of the ejection expelled out of the molten pit. The results indicate that the detection of acoustic emission can be used as a real-time online method to obtain information on the millisecond laser-induced damage.

Influencing Factors in Acoustic Emission Detection: A Literature Review Focusing on Grain Angle and High/Low Tree Ring Density of Scots Pine

Among non-destructive testing (NDT) techniques applied to structural health monitoring in existing timber structures, ranging from visual inspection to more sophisticated analysis, acoustic emission (AE) is currently seldomly used to detect mechanical stresses in wooden building assets. This paper presents the results from a systematic literature review on AE NDT applied to monitor micro and macro fracture events in softwood, specifically Scots pine. This survey particularly investigates its application with respect to the tree rings density and grain angle inspection, as influencing factors well correlated with physical and mechanical characteristics of wood. The literature review was performed in a three-step process defined by the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) flow diagram, leading to the selection of 31 documents from different abstract and citation databases (Scopus, Web of Science and Google Scholar). The outcomes have highlighted how laboratory experiments, including several types of tests (tensile, cutting, compressive, etc.), were conducted in most cases, while a very limited number of studies investigated on in situ monitoring. In addition, theoretical approaches were often explored in parallel with the experimental one. It emerges that—for tree ring density studies—a multi-technique approach, which may include microscopic observations, could be more informative. Indeed, although not widely investigated, high/low tree ring density and grain angle were found as influencing factors on the AE parameters detected by the sensors, during condition and structural health monitoring experiments.

Influencing Factors in Acoustic Emission Detection: A Literature Review Focusing on Grain Angle and High/Low Tree Ring Density of Scots Pine

Influencing Factors in Acoustic Emission Detection: A Literature Review Focusing on Grain Angle and High/Low Tree Ring Density of Scots Pine

AE Detection of Crack Extension of Ceramics under Thermal Shock and Characterization of Fracture Mechanics

The mixed mode crack extension behavior of ceramics under thermal shock was dynamically evaluated by a disc-on-rod test and AE measurement. In this test, the transient temperature distribution was measured by an infrared(IR) camera. The microfracture process was dynamically characterized by acoustic emission (AE) measurement, and the crack extension path were observed by a video camera. Using elliptical specimens and elliptical rods, mixed-mode crack extension behavior was characterized. Intermittent crack extension was observed as the temperature distribution changed, and AE signals were detected at the same time. The fracture mechanical parameter of the mixed mode crack extension behavior of ceramics under thermal shock were calculated by the finite element method using the temperature distribution measured by an IR camera. It was confirmed the R-curve behavior in which crack extension resistance increases with crack extension. Consequently, the fundamental insight for the integrity assessment of ceramic structures under thermal shock was obtained.

Change of Acoustic Emission Characteristics during Temperature Induced Transition from Twinning to Dislocation Slip under Compression in Polycrystalline Sn.

In this study, acoustic emission (AE) measurements on polycrystalline tin as a function of temperature at different driving rates under compression were carried out. It is shown that there is a definite difference between the acoustic emission characteristics belonging to twinning (low temperatures) as well as to dislocation slip (high temperatures). The stress averaged values of the exponents of the energy probability density functions decreased from = 1.45 ± 0.05 (−60 °C) to = 1.20 ± 0.15 (50 °C) at a driving rate of , and the total acoustic energy decreased by three orders of magnitude with increasing temperature. In addition, the exponent γ in the scaling relation SAE~DAEγ (SAE is the area and DAE is the duration) also shows similar temperature dependence (changing from γ = 1.78 ± 0.08 to γ = 1.35 ± 0.05), illustrating that the avalanche statistics belong to two different microscopic deformation mechanisms. The power law scaling relations were also analyzed, taking into account that the detected signal is always the convolution of the source signal and the transfer function of the system. It was obtained that approximate values of the power exponents can be obtained from the parts of the above functions, belonging to large values of parameters. At short duration times, the attenuation effect of the AE detection system dominates the time dependence, from which the characteristic attenuation time, τa, was determined as τa ≅ 70 μs.

Multichannel Detection of Acoustic Emissions and Localization of the Source with External and Internal Sensors for Partial Discharge Monitoring of Power Transformers

The detection of acoustic emissions with multiple channels and different kinds of sensors (external ultrasound electronic sensors and internal optical fiber sensors) for monitoring power transformers is presented. The source localization based on the times of arrival was previously studied, comparing different strategies for solving the location equations and the most efficient strategy in terms of computational and complexity costs versus performance was selected for analyzing the error propagation. The errors of the acoustic emission source location (localization process) are evaluated from the errors of the times of arrival (detection process). A hybrid programming architecture is proposed to optimize both stages of detection and location. It is formed by a virtual instrumentation system for the acquisition, detection and noise reduction of multiple acoustic channels and an algorithms-oriented programming system for the implementation of the localization techniques (back-propagation and multiple-source separation algorithms could also be implemented in this system). The communication between both systems is performed by a packet transfer protocol that allows continuous operation (e.g., on-line monitoring) and remote operation (e.g., a local monitoring and a remote analysis and diagnosis). For the first time, delay errors are modeled and error propagation is applied with this error source and localization algorithms. The 1% mean delay error propagation gives an accuracy of 9.5 mm (dispersion) and a maximum offset of 4 mm (<1% in both cases) in the AE source localization process. This increases proportionally for more severe errors (up to 5% reported). In the case of a multi-channel internal fiber-optic detection system, the resulting location error with a delay error of 2% is negligible when selecting the most repeated calculated position. These aim at determining the PD area of activity with a precision of better than 1% (<10 mm in 110 cm).

Tribological Behavior of NiTi Alloy Produced by Spark Plasma Sintering Method

The tribological behaviors of NiTi alloy produced by the spark plasma sintering (SPS) method before and after annealing were investigated at various loading conditions via indentation, scratch, and wear tests. Indentation tests were performed by a pyramidal Berkovich indenter, while scratch and wear tests were carried out by a diamond Rockwell spherical indenter at room temperature. The annealing of the as-prepared samples was performed at 350, 450, and 550 °C in the ambient atmosphere. The influence of the annealing temperature on the sample behavior towards tribological study was investigated here. The results indicated that the alloy annealed at 350 °C showed a higher hardness compared to the other annealed alloys. The scratch and wear resistance of the annealed sample at 350 °C showed a better performance in comparison to the other samples under a constant load. The high wear resistance of the annealed NiTi alloy may be attributed to its metastable R-phase. The detection and evaluation of acoustic emissions during the nano/micro-tribomechanical testing proved to be a very effective way for the exploration of the durability of SPS NiTi alloys.

Cavitation Study in Centrifugal Pumps Through Acoustic Signal Analysis

The cavitation phenomenon causes serious problems in centrifugal pumps, such as poor hydraulic performance and damage to the internal structure of the pump produced by material erosion. Additionally, cavitation induces vibrations and noises that do not occur under normal operating conditions. These changes can be used as a guide for the diagnosis of pumps. In this article, different criteria based on the acoustic signals emitted by a centrifugal pump are analyzed to identify its cavitation condition. For this, an experimental assessment, in which the pump operates in four different flow conditions, namely, 20 l/min, 40 l/min, 60 l/min, and 80 l/min, is performed. The detection of acoustic emissions has been carried out through a microphone located at a specific distance from the pump. The results have shown that the use of acoustic parameters such as Loudness, Crest factor, and Zero crossings calculated from the base sound signal, the derivative, and its log dt/dp value, allows the identification of three pump operation zones: one free of cavitation, the onset of cavitation and the fully developed cavitation condition. The study has concluded that acoustic emissions provide sufficient information to diagnose the presence of cavitation. Additionally, the methodology based on this type of signal has the advantage that it does not require high implementation costs, and it can be widely improved depending on the requirements.

DFB-FL Applied in the Liquid-Solid Composite Dielectric for Ultra-High Sensitive Partial Discharge Acoustic Emission Detection

The traditional fiber optic acoustic emission (AE) sensor, used to detect the partial discharge (PD) in the liquid-solid composite dielectric such as oil-immersed transformers, is not satisfactory in engineering applications due to the limitation of sensitivity and sensor size. This work proposes that the distributed feedback fiber laser (DFB-FL), benefiting from its tiny size and ultra-high sensitivity, is a better choice for PD AE detection. We build the PD AE detection system using erbium-ytterbium co-doped (Er-Yb-co-doped) DFB-FL, with suitable photoelectric components to design the demodulation system and intensity noise of DFB-FL as an index. Noise analysis shows that the average noise amplitude of the system is reduced by 91.67% after digital filtering technology and pump laser power regulation technology. We also use an 80 kVA oil-immersed transformer winding structure to construct a liquid-solid composite dielectric PD AE detection platform. Moreover, experiment results in different pump power show that the DFB-FL PD AE detection system can effectively detect the PD AE signal in the environment with sizeable acoustic impedance. The peak-to-peak value of its response is 31.36 times larger than the background noise and 637% higher than piezoelectric transducer sensors (PZT).

Combining active and passive acoustic methods to image hydraulic fracture growth in laboratory experiments

We combine active and passive acoustic measurements to improve the spatio-temporal imaging of hydraulic fracture growth performed under true triaxial confinement in the laboratory. 64 active piezo-electric transducers (54 P waves, 10 S waves) work in source (32) - receivers (32) mode to perform an acoustic survey at repetitive intervals (every 10 seconds) during a hydraulic fracture growth experiment. The analysis of the evolution of the active acoustic monitoring changes allow to image the evolution of the fracture front (via an inversion of the active acoustic waves diffracted by the fracture front). An additional 16 piezoelectric transducers are pre-amplified and work in passive mode continuously recording at 10MHz. We present a nearly-automatic passive signal processing, acoustic emission detection, and location algorithm. This allows to record, detect and to locate acoustic emissions associated with fracture initiation and growth in between the active acoustic measurement sequences. Using a hydraulic fracturing test performed in gabbro, we discuss how active and passive acoustic monitoring complements one another and bring different type of information on hydraulic fracture growth.

Evaluation of Adhesion Properties of Hard Coatings by Means of Indentation and Acoustic Emission

In general, the mechanical properties of hard thin coatings are investigated using indentation methods. Material characteristics of hard coatings, such as elastic modulus and hardness, are evaluated by means of nanoindentation and an appropriate evaluation methodology. The most popular method used to obtain the coating properties required using nanoindentation is the evaluation based on the Oliver and Pharr methodology. Adhesion and wear properties can be calculated using these data. In this study, we used a novel method to evaluate the wear and adhesion of coatings. A special measuring device combined with static indentation and acoustic emission signal detection was developed to evaluate the adhesion of coatings. The device consists of a macrohardness instrumental indentation device equipped with an acoustic emission measuring gauge. It was used to investigate crack formation and adhesion of coatings deposited on different substrates using acoustic emissions data. The results using both the existing and novel methods were compared and evaluated.

Failure mechanism of Ω-shape 3D orthogonal woven composite component under transverse low-velocity impact and subsequent axial compression load

Failure mechanism of complex profile component is always different from that of conventional plate counterpart due to the coupling effect of material and structure. In this work, the low-velocity impact (LVI) and compression after impact (CAI) behaviors of Ω-shape hybrid carbon/Kevlar 3 D orthogonal woven (3DOW) composite made for vehicle B-pillar were comprehensively studied by mechanical tests and mesoscale finite element (FE) analysis at component level, high-speed infrared (IR) thermal imaging, acoustic emission (AE) detection, and microscopic damage morphology characterization. It is found that a through-thickness stress concentration ring leads to high stress state and damage zone penetrating from the impact side to non-impact side along the ring path instead of at the lowest impactor position. The slope effect can not only help the stress conduction downward, but also inhibit the damage propagation from the impact side to the slope. Impact-induced cracks are concentrated around the R corners and extended along the axial direction of the specimen, forming the strip-shaped damage concentration zone along the upper eave of the slope. The Progressive Top-Down Crushing (PTDC) mode of compression after impact is due to the complex deformation process of each yarn such as squeezing, folding and eversion in the crushing process from the top of specimen. And the Middle Indentation Fracture (MIF) mode is the result of bending instability and abrupt fracture. This work presents a reference significance for the further development of composite strengthening components in vehicle bodywork.

Large dynamic-range fiber Bragg grating sensor system for acoustic emission detection.

A distributed feedback (DFB) fiber laser and fiber Bragg gratings (FBGs) are configured to demodulate the wavelength shifts of FBG dynamic strain sensors. The FBG sensors act as sensing units to detect the dynamic strain and the demodulators while the DFB fiber laser only acts as a narrow-linewidth light source. As the reflective spectrum of the FBG sensor changes due to dynamic strains, the output is subsequently converted into a corresponding intensity change and detected directly by a photodetector. The 0.2 nm linewidth FBG sensor can detect the impact signal with a frequency of up to 300 kHz with a maximum of 29.17 µɛ, which is comparable with the detecting result of the piezoelectric transducer sensor. Moreover, the directional response of the FBG sensor is maximized when the direction of acoustic wave propagation is parallel to the optical fiber. The relation between the sensitivity and the FBG spectrum linewidth is presented, and the detectable strain range versus different FBG linewidths is also discussed.

Experimental Study of Creep Acoustic Emission Characteristics of Coal Bodies around Boreholes under Different Moisture Contents

Water content is an important factor in the deformation-destruction process of coal bodies. To analyze the influence of water on the creep acoustic emission (AE) characteristics of coal rock surrounding a borehole, we conducted graded loading creep AE tests of single-hole specimens with different water contents (0%, 4%, 8% and water-saturation) under uniaxial loading. The findings include the following: the water content affects the creep mechanical properties of the coal body around a borehole. The creep transient strain and steady-state strain increased exponentially with rising water content; the saturated specimen showed the highest increase, reaching 44.5% and 28.6%, respectively. The specimen water content affected the cumulative ringing count (CRC) and the axial strain during creep. The axial strain increased with rising water content, the CRC increased linearly with rising axial strain. The higher the water content, the greater the CRC rise. At different stress levels, the CRC in the 4%, 8% and saturated water content specimens changed by 43%, 53% and 74%, respectively. The AE ringing rate showed a pattern of grow–decline–stabilize at each creep stage. The AEs decreased significantly with the rising water content and the creep curve lagged behind the AE data. This paper provides guidelines for gas extraction, borehole maintenance and AE detection.

Real-time Monitoring of Fluidized Bed Agglomerating based on Improved Adaboost Algorithm

Absctract: In order to to detect the polymer agglomeration in fluidized bed reactor (FBR), a method of real-time monitoring of agglomeration in fluidized bed polyolefin reactor based on voiceprint feature recognition is developed. First, the acoustic emission detection technology is applied to collect the acoustic signal generated by the polymer collision on the inner wall of FBR. Then, the voiceprint features of the collected acoustic signal are extracted with the Mel Frequency Cepstrum Coefficients (MFCC) and the Linear Prediction Cepstrum Coefficients (LPCC). To classify the extracted voiceprint features, an improved Adaboost algorithm is proposed to establish the real-time agglomeration classification model. Due to the introduction of cost factor and Gini index decision-making calculation to the Adaboost algorithm, the proposed improved Adaboost algorithm can classify unbalanced small samples with better accuracy and F-score index compared with the traditional Adaboost algorithm. The experiment results in a fluidized bed pilot plant have verified the effectiveness and feasibility of the proposed method.

Crack identification and evaluation in BEoL stacks of two different samples utilizing acoustic emission testing and nano X-ray computed tomography

A novel approach is presented to evaluate the mechanical stability of back end of line (BEoL) stacks. A SRAM test vehicle manufactured in 28 nm technology with copper pillar bumps is used. In a second step, the validity of the approach is also shown for a second sample manufactured in 22 nm technology and the experimental results are compared. To inflict damage to the BEoL stack of the respective semiconductor device, external forces are applied to the copper pillars (Cu-pillars) by shear loading using a tribo-indenter system. An acoustic emission (AE) detection sensor is attached to the sample to measure acoustic waves during the shear experiment as an indication for damage. The damage progression in the BEoL stack is extremely fast, hence details can't be resolved anymore with the piezo sensors of the tribo-indenter. However, due to the much higher temporal resolution, AE measurements give a more precise insight into the damage process. The resulting damages are imaged using nano X-ray computed tomography (nXCT) as well as scanning electron microscopy (SEM). The results provide a better understanding of the origin and the propagation of damages in the BEoL stack.

Influence of grouted sleeve and concrete strength of fabricated shear wall on acoustic emission detection method for sleeve compactness

It has been verified by relevant studies that the nondestructive detection method combining acoustic emission (AE) technology and signal generator can be used to detect sleeve grouting compactness of fabricated shear wall. However, sleeve material, grout type and concrete strength will affect the results of the above detection method. In this paper, the influence of these characteristics on the AE detection method for sleeve compactness was studied. The results show that the amplitude and energy of carbon steel sleeve are not much different from those of nodular cast iron sleeve. In contrast, the amplitude and energy of bellows sleeve are much smaller. Compared with the sleeve material, the volume and shape of the sleeve have a greater impact on the AE signal. The AE signal can be affected by the grout types. The amplitude and energy of the more compact UJOIN-108 grout are respectively 68.4 dB and 29.5 mV*ms. which are greater than those of BY(S)-YJ85 grout with 67.4 dB and 19.5 mV*ms. As the concrete compressive strength of the fabricated shear wall specimen increases from 48.5 MPa to 51.6 MPa, the amplitude and energy of AE signal increase accordingly. The amplitude and energy of AE signal of the specimens with high-strength grouting material and high-strength concrete are larger, and the AE signal is characterized by the same law. The frequency of AE signal is very effective in characterizing the change of sleeve material and concrete strength, but it does not perform well in characterizing the change of grout types.

Research on Coal Mechanical Properties Based on True Triaxial Loading and Unloading Experiment

To study the safety issues caused by coal mine excavation, self-developed simulation of earth interior atmosphere and sound test system was used to perform true triaxial loading and unloading tests of coal. An acoustic emission detection system was used to record the damage evolution trend of coal under different intermediate principal stress states. The experimental results show that in the true triaxial unloading test, as the intermediate principal stress increases, the failure state of coal changes from shear failure to partial shear tension failure, finally leading to overall yield failure. In the stress-strain curves, with the increase in intermediate principal stress, the strain in the direction of intermediate principal stress gradually changes from compression to expansion, and typical expansion occurs. The Mogi–Coulomb strength criterion better reflects the strength failure characteristics of coal during unloading. The stress-acoustic emission diagrams show that the increase in intermediate principal stress causes the internal cracks of the coal to grow unsteadily and exponentially, and the increase in intermediate principal stress makes the coal lose its ability to continue to bear the load. Studying the influence of the intermediate principal stress on the mechanical properties of coal has practical significance for coal mine safety production.