Acoustic Emission Measurements Research Articles

Material defects detection based on in-process measurements in milling of Ti6246 alloy

An increasing demand for products and services in the aviation industry is attended by a rising demand for aircraft engines. This requires an increased productivity combined with highest quality and safety standards. In this paper, a new approach of material defect detection is presented which is based on force and acoustic-emission measurements during machining processes. Representative synthetic defects in titanium alloy Ti6246 were investigated. In order to use scale effects, the experiments were conducted in micro-milling processes. This approach could be used for an automated, non-destructive evaluation of the manufactured components in the future and thus for reducing testing effort and related auxiliary times.

Acoustical Characteristics of Proton Exchange Membrane Fuel Cells

In order to optimise the performance of Proton Exchange Membrane Fuel Cells (PEMFCs) and to maximise their life cycle, water content has to be properly controlled. This paper presents a model-based method to determine the effect of load on PEMFC water content in PEMFCs using Acoustic Emission (AE) measurements. The developed model was implemented in COMSOL and verified using a single proton exchange membrane fuel cell (FC) operated under various loads. Acoustical events originating from water bubble formation have been identified and assessed using statistical parameters determined in the time and frequency domains. The feasibility of using AE techniques to detect and monitor the impact of a cell's load variation on water content is assessed. As the model results were in good agreement with experimental data, it was concluded that an AE based method could serve as an effective monitoring and control tool of water content in PEMFCs. Statically, the root mean square for acoustic emission activity has a significant relation with load characteristics and can, potentially, be a candidate for determining the AE behavior in a PEMFC.

Applicability of the Specimens with Holes Aligned to the Polygonal Line that Cause Acoustic Emission for Evaluating Acoustic Emission Measurement Systems

Applicability of the Specimens with Holes Aligned to the Polygonal Line that Cause Acoustic Emission for Evaluating Acoustic Emission Measurement Systems

Music of grain crushing with the Discrete Element Method

A series of compression tests on agglomerates of microspheres representing a single grain are conducted to investigate the impact of heterogeneity on the acoustic emissions (AE) generation. The grain heterogeneity is realized by using a Weibull shape parameter-augmented traditional discrete element method (DEM). During the compression process the development of the micro-cracks, and the magnitude and location of the AE events are tracked and recorded. Through a 3D visualization of the AE events, their location and the clustered broken bonds are identified. The current study demonstrates the potential of AE measurements to track changes in the fabric and structure of granular materials. The results of this DEM study will contribute to clarify the mechanism of particle breakage and its consideration in practical applications.

Analysis of tensile behavior of recycled aggregate concrete using acoustic emission technique

Recycled concrete aggregate (RCA) was processed from reinforced concrete edge beams sourced from a demolished bridge. This material replaced different ratios of coarse aggregate in a benchmark concrete. The tensile behavior of the developed concrete mixes was characterized via monotonic and cyclic uniaxial tensile tests performed on notched cylinders. Such tensile tests allow for the quantification of the fracture energy and softening behavior of the concrete. Moreover, acoustic emission (AE) measurements were conducted in conjunction with the cyclic tests to characterize e.g. micro-crack initiation and development, as well as crack localization. The tensile behavior of the various materials was found to be similar with minimal variation in the results. However, the softening behavior suggests that the RCA materials are slightly more brittle compared to both the mother and benchmark materials. The corresponding AE measurements also indicated similarities between the micro-crack initiation and development for these mixes. It can be constituted that if the concrete used to produce RCA is of high quality and from one source, the resulting RAC will have adequate tensile properties with minimal variation, despite the aggregate replacement ratio.

Acoustic emission as a tool for prediction of nugget diameter in resistance spot welding

Acoustic emission monitoring has been successfully employed in different application areas such as monitoring of fatigue loaded bridges and pressure testing of vessels. However, application of this technology on resistance (spot) welding processes yielded limited results. Existing literature only mentions the detection of certain defects such as expulsion and cracked welds. Detecting nugget nucleation and growth, to allow prediction of nugget diameter, has never been proven to be feasible based on acoustic emission signals. This work contains experiments based on varying as well as constant nominal welding parameter sets, where acoustic emission waveforms were collected during the welding process. A methodology is described, revealing a correlation between certain frequencies present in the acoustic emission signal and physical events occurring during welding. Based on these frequencies, a model is constructed for predicting the nugget diameter of resistance spot welds based on acoustic emission measurement data.

Instrumented Hip Implant: A Review

About 20% of people older than forty years old face more bone degenerative diseases. The older population is increasing quite rapidly than before which increases the need for knee or hip implants tremendously. One of the major problems of the current implants is their short lifetime and their impact on the surrounding human tissue. The short life can be attributed to implant wear, loosening, and misalignment, which often cause pain and discomfort to the patient. Functional failure of the implant may be followed by a revision surgery, which is often painful and has a relatively low success rate. Moreover, to avoid unexpected failure and unnoticed deterioration of the implant, it is important to make provision for monitoring implants' performance. Instrumented implants can provide accurate monitoring of the loosening state of the implant, which can delay the revision surgeries and its consequences. This study provides a comprehensive review of the technological development of instrumented hip implants to monitor the status of the implants. The main requirements for the implants are highlighted by reviewing different aspects of the instrumented hip implant systems. In-vivo studies reported in the literature were summarized. Vibration and Acoustic Emission (AE) measurement based loosening detection were found to be the most common methods for in-vitro studies. A comprehensive review of power supply and communication modules was presented. Despite the advancement in this field, current systems are not yet able to provide effective monitoring of the implant's status during the daily activities of patients.

Acoustic emission diagnostics of corrosion monitoring in prestressed concrete using hidden Markov and semi-Markov models

This article presents a framework based on hidden Markov modeling for monitoring corrosion damage in prestressed concrete structures through acoustic emission measurements. Both hidden Markov models and hidden semi-Markov models are investigated to determine the merits of each under typical challenges encountered in real-world monitoring scenarios: an unknown initial corrosion condition and an uncertain corrosion rate. To enable hidden semi-Markov models to perform effectively, they are constructed using extended state hidden Markov models in a manner which is able to easily accommodate these scenarios. Furthermore, a framework is proposed for adopting frequency- and topological-based features of acoustic emission data as indicators of corrosion for the models. Accelerated corrosion tests were carried out on two prestressed concrete specimens; one specimen was used for training the models and the other one for testing. The testing specimen was additionally subjected to accelerated weathering to approximate certain conditions found in the field. A combination of established visual inspection, mass loss measurement, and acoustic emission activity analysis was first used to obtain a benchmark corrosion assessment of the specimens. Frequency- and topological-based acoustic emission features were then used as the basis of the hidden Markov modeling framework. The results demonstrate that both hidden Markov models and hidden semi-Markov models are highly reliable under an unknown initial condition. However, in these tests, the hidden semi-Markov model showed slightly greater reliability against error in the assumed corrosion rate. To improve accuracy in this scenario, a procedure for combining predictions from various candidate corrosion rates was also proposed. The diagnostics obtained from this work may provide useful information for established prognostic models of corrosion mechanisms in prestressed concrete.

Criticality Hidden in Acoustic Emissions and in Changing Electrical Resistance during Fracture of Rocks and Cement-Based Materials.

Acoustic emissions (AE) due to microcracking in solid materials permit the monitoring of fracture processes and the study of failure dynamics. As an alternative method of integrity assessment, measurements of electrical resistance can be used as well. In the literature, however, many studies connect the notion of criticality with AE originating from the fracture, but not with the changes in the electrical properties of materials. In order to further investigate the possible critical behavior of fracture processes in rocks and cement-based materials, we apply natural time (NT) analysis to the time series of AE and resistance measurements, recorded during fracture experiments on cement mortar (CM) and Luserna stone (LS) specimens. The NT analysis indicates that criticality in terms of electrical resistance changes systematically precedes AE criticality for all investigated specimens. The observed greater unpredictability of the CM fracture behavior with respect to LS could be ascribed to the different degree of material homogeneity, since LS (heterogeneous material) expectedly offers more abundant and more easily identifiable fracture precursors than CM (homogenous material). Non-uniqueness of the critical point by varying the detection threshold of cracking events is apparently due to finite size effects which introduce deviations from the self-similarity.

Non-linear distributions of bond-slip behavior in concrete-filled steel tubes by the acoustic emission technique

This study aims to investigate the non-linear distribution of bond-slip behavior in steel-concrete interface of concrete-filled steel tubes (CFST). An analytical model was proposed to account for the attenuation effect in boundaries of load transfer. In this analysis, a modified governing equation with the second-order ordinary differential form was deduced on the basis of elastic theory. Solutions of slippage, bond stress and potential energy in the steel-concrete interface were then obtained. For the model validation, measurements of acoustic emission (AE), as well as strain gauge, were performed in a push-out test of CFST. Test results agree well with the solutions of the analytical model proposed. The interfacial bond stress exhibits a highly non-linear distribution along the direction of load transfer. The maximum stress appears nearby the position of 0.2L away from the specimen end, and is about 1.2 times of the average shear strength in steel-concrete interface. In addition, the AE peak frequencies of bond failure have two main bands, including 75–125 kHz and 290–340 kHz. It indicates that there are mainly two failure modes during the debonding of steel–concrete interface in CFST.

Investigation of signal behaviors for sensor fusion with tool condition monitoring system in turning

Monitoring of the cutting area with different type of sensors requires confirmation for composing sensor fusion to obtain longer tool life and high-quality product. The complex structure of machining and interaction between variables affect the influence of parameters on quality indicators. Using multiple sensors provide comparison of information acquired from different resources and make easier to decide about tool and workpiece condition. In this experimental research for the first time, five different sensors were adopted to a lathe for collecting data to measure the capability of each sensor in reflecting the tool wear. Cutting forces, vibration, acoustic emission, temperature and current measurements were carried out during turning of AISI 5140 with coated carbide tools. Considering the graphical investigation, the successes of sensors on detection of progressive flank wear and tool breakage were investigated. Besides, the effects of cutting parameters on measured variables were interpreted considering graphs. According to results, temperature and acoustic emission signals seem to be effective about 74% for flank wear. In addition, fuzzy logic based prediction of flank wear was performed with the assistance of temperature and acoustic emission sensors with high accuracy which demonstrates their availability for sensor fusion. Tool breakage occurs instantly which can prevent with the assistance of sensor signals and tangential and feed cutting forces, acoustic emission and vibration signals seem as reliable indicators for approaching major breakage. Sensor fusion based turning provides confirmed information which enables more reliable, robust and consistent machining.

Study on the characteristics of magneto acoustic emission for mild steel fatigue.

Fatigue life of materials or structures can be classified into three stages: fatigue hardening or softening, crack initiation and crack propagation, which includes two stages. Current mature non-destructive testing (NDT) methods can only detect macro or visible cracks in stage II crack propagation. In order to detect and evaluate the fatigue damage occurring before stage II crack propagation quickly and effectively, magneto acoustic emission (MAE) measurement was carried out on laboratory specimens with different numbers of fatigue cycles. With the accumulation of fatigue damage, the RMS of MAE decrease steadily on the whole, making MAE a promising non-destructive method for evaluating fatigue damage. To make MAE applicable in noisy environments, square waveform voltage were selected to excite magnetic fields, and 'T' type MAE signals with higher amplitude were produced. The variation of MAE with number of fatigue cycles at different excitation intensity indicated that the defects associated with fatigue damage have greater effects on the creation and annihilation of domain walls. The point where the MAE amplitude begins to increase instead of decrease with fatigue can be an indicator for the onset of stage II crack propagation. This article is part of the theme issue 'Advanced electromagnetic non-destructive evaluation and smart monitoring'.

Structural condition assessment of reinforced-concrete bridges based on acoustic emission and strain measurements

A reliable novel monitoring approach is developed to assess the structural condition of reinforced-concrete bridge elements. The approach is based on combining acoustic emission technique and strain gauge measurements, and it is illustrated by a case study of a composite steel–concrete viaduct in service since 1957. Monitoring was performed on its reinforced-concrete deck slab under traffic and environmental loading for one year. The monitoring setup and procedure are presented. The variation of acoustic emission signals is evaluated regarding strain and temperature measurements. Parametric study, pencil-break test, statistical analysis, crack classification and b-value analysis are performed to assess the structural condition. The acoustic emission activity of the reinforced-concrete slab is evaluated for 1 year under operational conditions. From the monitoring approach, it was possible to identify the nature of the cracking activity in the concrete slab as a function of traffic loading and temperature and to assess in time the condition of the slab-girder connection.

All-Fiber Laser-Self-Mixing Sensor for Acoustic Emission Measurement

Self-mixing interferometry (SMI) is a promising non-destructive sensing technology with advantages of simplicity in system structure, low cost in implementation, ease in optical alignment, and high resolution in measurement. It consists of a laser diode, a photodiode packaged at the rear of the laser diode, a lens, and a target to be measured. Typically, SMI-based sensing is to measure the phase change in an SMI signal with a fringe pattern as sinusoidal or saw-tooth like. The phase is called optical phase in external cavity that is linked to the quantity to be measured, e.g., displacement, velocity, and vibration. Each SMI fringe maps to a half-laser-wavelength displacement of the target. With increasing feedback level in an SMI system, some fringes may lost or even totally disappear. In this case, the laser output from an SMI system can trace the optical phase to achieve a linear sensing relationship. In this article, we design an all-fiber SMI linear sensor for real-time and fast tracking acoustic emission (AE) signals. Firstly, a system design in terms of selection of operating parameters is presented. Then, a proof of concept experimental system was built for detecting AE signals. The results show that the proposed SMI sensor has comparable AE detection capability to piezoelectric sensor, providing a compact and cost-effective optical AE sensing solution without need of extra signal processing, which can be considered as a viable alternative to the well-established piezoelectric AE sensor.

The effects of micro- and meso-scale characteristics on the mechanical properties of coal-bearing sandstone

Studying the effects of the micro- and meso-scale characteristics of coal-bearing sandstone on its mechanical properties can provide basic data and accumulated experience for the development of technology for the in situ testing of the strength of rock masses. In this paper, the micro- and meso-structures, mineral composition, and elemental contents of 16 kinds of sandstone from three coal mines were studied through X-ray diffraction and polarizing microscope analysis. The stress–strain evolutional characteristics of different sandstone samples were obtained through uniaxial compression, tension, and shear tests under acoustic emission monitoring, and the effect of various micro- and meso-characteristics on the mechanical properties and failure characteristics of the sandstones was investigated. The results show that the strength, elastic modulus, cohesion, and friction coefficient all increase with increasing quartz content and degree of particle contact, and decrease with increasing plagioclase and clay mineral content, especially kaolinite content. The failure mode of sandstone samples is mainly shear failure during uniaxial compression, the larger the particles and the lower the quartz content, the higher the RA value generated near the peak, indicating that more tensile failure occurs. Furthermore, the strength damage model and damage constitutive model are established by acoustic emission measurement data. These results could provide useful reference for the development of intelligent systems for the in situ testing of the mechanical properties of coal and rock masses.

Acoustic emission behavior of granular soils with various ground conditions in drained triaxial compression tests

Since the mechanical failure of granular soils is the macro-manifestation of complex internal particle interactions, studying this relevant issue from micro-scale perspective is of fundamental importance. Acoustic Emission (AE) has become a promising approach for this purpose; however, its synthetic and validating study on granular soils with various ground conditions is far from substantive. In an attempt to verify and correlate the relationship between AE behaviors and mechanical behaviors of granular soils with various conditions, results of drained triaxial compression tests along with AE measurements recorded during testing are discussed. These results revealed intrinsically different propagation properties of acoustic waves between saturated and unsaturated/dry sands. The water in saturated sands facilitates acoustic waves to propagate with less attenuation, whereas discontinuities (i.e. particle-particle contacts and particle interfaces with water) in dry/unsaturated sands lead acoustic waves to propagate with larger attenuation. The AE manifestation showed its high sensitivity to different saturation degrees, package densities and confining stress levels, which allows the evaluation of ground conditions to be made by AE. The congruous AE evolution in saturated sands was considered closely related to particle interactions during drained triaxial compression; whereas the changeable AE evolutions in accordance with different failure patterns in dry sands were considered relating to soil structure behaviors.

Evaluation of Weak Bonds in the Interface of a Single Lap Joint for Carbon-Fiber Reinforced Plastic Adherends Using Acoustic Emission Measurement

Evaluation of Weak Bonds in the Interface of a Single Lap Joint for Carbon-Fiber Reinforced Plastic Adherends Using Acoustic Emission Measurement

The Sound of Batteries: An Operando Acoustic Emission Study of the LiNiO2 Cathode in Li–Ion Cells

AbstractThe development of advanced Li‐ion batteries relies on the implementation of high‐capacity Ni‐rich layered oxide cathode materials, such as NCM and NCA, among others. However, fast performance decay because of intrinsic chemical and structural instabilities hampers their practical application. Hence, thoroughly understanding degradation processes is crucial to overcome current limitations. To monitor instabilities of electrode materials under realistic operating conditions, the application of nondestructive operando techniques is required. While structural changes of crystalline phases can be studied by X‐ray diffraction, microstructural changes (e. g., particle fracture) cannot be easily accessed in situ and are therefore mostly investigated ex situ. Here, we use acoustic emission (AE) measurements to probe a potential next‐generation cathode material in real‐time. Specifically, we focus on LiNiO2 (LNO) and demonstrate that AE events in different frequency ranges can be correlated with the formation of the cathode solid‐electrolyte interphase and the mechanical degradation during electrochemical cycling.

Effect of cavitation and free-gas entrainment on the hydraulic performance of a centrifugal pump

An experimental study on gas–liquid two-phase flow characteristics in a low-specific-speed centrifugal pump is presented via employing multiple investigation techniques, such as visualization observation, measurements of acoustic emission and vibration, etc. Specially, three different flow conditions were inspected, namely gas locking initiation, critical cavitation with/without free-gas presence, etc. For gas locking, the drastic deterioration of the pump performance and the disrupted balance of shaft were observed. Especially, at low rotational speeds, the gas locking accompanied with intermittent or churn flow can be triggered by even lower inlet gas volumetric fractions. When it came to the cavitation flow, a small amount of gas entrainment could induce the rapid deterioration of cavitation and stimulate much higher amplitude in low-frequency band of shaft rotation. The relationship between the gas bubble trajectory and the vibration level under the backflow is discussed. The results reveal that the combined effect of the free-gas entrainment and cavitation on the pump instability is much stronger than that under natural cavitation or free-gas entrainment flow, whose fault diagnosis can be determined by the data manifested in different spectral segments.

Effect of Chemical Aggressive Media on the Flexural Properties of Cured-In-Place Pipes Supported by Microstructure Observation and Acoustic Emission.

The cured-in-place pipe (CIPP) method is currently the most frequently used approach for the renovation of piping without digging; this technology is suitable for pipes made from all types of material. The authors of this paper examined how chemical substances and increased temperature change samples of CIPP with vinyl-ester resin taken from a simulated installation. Changes were observed at several levels: visually via a digital optical microscope, through changes of short-term bending properties and by observation of the activity of the sample structure by means of acoustic emission (AE). Interdependencies among the observed parameters were examined, specifically, the cumulative number of hits (cnt)/deflection and flexural properties/mechanic wave velocity. The test results prove that after three weeks of immersion in a simulated aggressive environment that mirrors what may happen to CIPP in real conditions, short-term mechanical properties change. This is also proven by the results of the AE measurements. For clarity, the results include images from a digital optical microscope. In addition, this paper proves that CIPP samples have good resistance to the action of organic and inorganic acids and to increased temperatures. After three weeks of exposure to a temperature of 100 °C the CIPP flexural properties of the samples had even improved.