EWGAE35 & ICAE10 Conference on Acoustic Emission Testing, Ljubljana, Slovenia, September 2022

Stresses born in the solid state may trigger acoustic emission (AE). Stresses are traditionally caused by mechanical forces and/or pressures implemented to the surface of the material. However, inner stresses in solid state may be born due to changing of magnetic field or due to temperature changes especially when cooling down the material, for example in structure changing. It is also well known that elongation of material structures due to rolling may lead to different AE bursts, which may be used for characterization of the structure of material due to cold forming. In the presentation we show in experiments that alternating magnetic field leads to AE burst, which have larger magnitude where the gradient of the changes of magnetic field is larger in absolute value. We also demonstrate correlation of the RMS of AE signals with the direction of the elongation of steel structure. This opens the way to investigate anisotropy in steel sheets. We also investigated the dependence of the measure of acoustic emission on frequency and on different sinus, triangle and rectangle forms in alternating magnetic field. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

    

   

The application of the AE technique in the field of civil engineering requires overcoming various issues related to several factors such as structure complexity, material nonhomogeneity, signal attenuation, environmental noise. In this concern, multivariate statistical analysis was successfully applied to manage AE data and discriminate relevant features related to main damage mechanisms in concrete. Principal component analysis (PCA) and artificial neural networks (ANN) were applied with promising results. However, a fundamental limitation of these numerical methods is that they are not user-friendly and their application requires suitable scientific expertise. In such a context, the development of an easy de-noising protocol, able to simplify the AE data analysis for damage structure assessment and failure prediction, is a fundamental improvement toward the applicability of this technology on real-scale concrete structures. In the present paper, the analysis of AE data collected during loading and unloading cycles up to the failure on a real scale post-tensioned concrete beam is reported. Different denoising approaches were adopted to remove a large incoherent AE population originating from the friction of hydraulic actuator steel plate on concrete surface and friction on beam supports during loading/unloading steps. Filtered data were then synchronized with the beam deformation and crack width opening. De-noising algorithms have then been validated by structure damage severity assessment using statistical indexes such as calm ratio, load ratio, severity, and historical index. The procedure was tested with interesting results on PT concrete beams characterized by different pre-existing damages on steel tendons. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

    

   

Damage localization is a relevant issue in structural health monitoring (SHM) of concrete structures. A greater level of insight into the structure can be so reached enabling more informed maintenance decisions and reducing operation and maintenance costs. The basic approach to acoustic emission localization, which is often referred to as the Time of Arrival (TOA) method, is based on detecting an AE source at a number of spatially-distributed sensors. However, in anisotropic media such as reinforced concrete, the basic assumptions for the TOA method become largely invalid. Different robust methods suitable to anisotropic media, incorporating an angular-dependent velocity term into the minimization process have been developed in the past. However, the wave-velocity profile is not always known. More recently a number of other authors have adopted various Bayesian approaches as part of AE localization strategies, including the use of a Markov chain Monte Carlo inference scheme as well as nonlinear Kalman filters. The use of a probabilistic approach in source location has become increasingly applied for AE source localization in complex large structures. In heavy reinforced post-tensioned concrete structures acoustic wave path can be significantly influenced by rebars as well as metallic post-tensioning ducts. Cracks opening can further influence acoustic propagation paths and greatly influence the reliability of AE source localization algorithms. In the present paper, different localization procedures have been developed and tested on post-tensioned concrete beams during loading and unloading cycles as well as on small homogeneous concrete blocks. In a highly emissive environment, significant difficulties have been reported also in event identification thus further reducing localization procedure reliability. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

    

   

Corrosion causes enormous damage to mechanical structures in many industrial sectors, and the aviation industry is no exception. To extend the lifetime of airframes without compromising safety, it is very important to have a clear picture of the state of corrosion (SoC) of the aircraft. Thus, it is essential to develop methodologies suitable for real-time monitoring of the SoC and subsequent reliable notification when a structure has been compromised by corrosion. Published results so far suggest that the ultrasonic (e.g. acoustic emission, guided waves) as well as electrochemical sensors (e.g. electrochemical noise, impedance spectroscopy) are suitable for monitoring aircraft-relevant corrosion but lack the technological readiness to be applied in commercial aircraft yet. A huge issue in achieving reliable monitoring systems is the correlation between corrosive phenomena and (typically) noisy sensor data. The AICorrSens project addresses these issues by developing a multisensor setup for monitoring the SoC based on ultrasonic, electrochemical, and environmental sensors coupled with AI algorithms. Training data shall be generated by performing accelerated corrosion tests with coupons and demonstrator parts equipped with sensors. Using AI for the subsequent data analysis, one can overcome operational noise, and thus, allow today’s corrosion detection methods onboard real- time evaluation of the SoC in terms of detection, localization, quantification, and typification. The ambition of the project is to transform the created continuous stream of data into classifications of the SoC that are intuitively understandable through a human-machine interface, including a qualified corrosion prediction by the AI models generated from test campaigns. The project results shall lead to increased aircraft safety and reliability and deliver a clear economic benefit for aircraft operators as it allows a switch from regular inspection intervals to condition-based maintenance. Funded by: Austrian Research Promotion Agency Program: Take Off, Call 2019 Consortium: CEST Competence Centre for Electrochemical Surface Technology (CEST), Johannes Kepler University Linz – Institute of Structural Light-weight Design (IKL), Danube University Krems – Department for Integrated Sensor Systems (DISS), Senzoro GmbH (SENZ). Project duration: 10/2020 – 09/2023. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

    

   

Studies show that 5-10% of industrial valves are suffering from internal leakage which can lead to economic losses, health and safety issues or potentially to contamination or environmental pollution. Acoustic emission is an established technology to inspect valves for internal leakage. Despite the successful establishment of the acoustic emission technology, current solutions have shown some limitations. These are e.g. their complexity of use, the need of trained and experienced personnel, the time required to perform analyses and the use of solely proprietary and closed devices. Experts performing inspections in the field are facing challenges such as using the right measuring points, flow noise from nearby processes, finding the right duration of measurement and interpreting the results. Research has shown that interpretation of results depends very much on experts’ know-how and reproducible results have thus been difficult to achieve. This causes difficulty for companies to use the data for further purposes, such as predictive maintenance. In order to tackle that problem, Senseven has taken over 1000 measurements in laboratories together with more than 10 different valve manufacturers during the last year. To replicate real production situations, leakages were also simulated in the field, taking into account different media/pressures/different valve sizes/nominal diameters and valve types. The experience gained and the data collected were used to build a digital and smart inspection system based on an artificial neural network. The challenge was to build a system that could generate reproducible results, analyze data automatically and store it in such a way that companies could use it for predictive maintenance purposes. In our technical paper session, we would like to discuss the advantages of using acoustic emission for valve inspection as well as outline the current challenges companies and inspection service providers face when performing measurements. We will discuss our findings from the field simulations and present our artificial intelligence approach for automatic leak detection and leak rate estimation. In addition, we will demonstrate our Acoustic Emission Platform and how it helps companies collect and store acoustic emission data in a structured and organized manner, taking another step towards a more efficient testing process. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

    

   

Acoustic emission monitoring is a useful method to deal with detection and identification of damage in composite materials during mechanical tests. From an experimental point of view, it is not straightforward to establish a quantitative link between the damage sources and AE signals. Modeling and numerical simulations appear as a promising way to reach this objective. In this study, Finite Elements Modeling (FEM) was used to simulate AE signals due to fiber break and fiber/matrix debonding in a model carbon fiber composite. A specimen made of a single carbon fiber and epoxy matrix was used to experimentally validate the simulated fiber break AE signals. The objective was to compare the AE signals from a validated fiber break simulation (Fig. 1a) to the AE signals obtained from fiber/matrix debonding (with several models) and fiber break obtained in several media and to discuss the capability to detect and identify each source (Fig. 1b). The influence of the type of sensor, specimen geometry and AE source location were also studied. The proposed model was extended to identify the main parameters that influence the acoustic emission signatures. These validated results open the way to combine the experimental and the simulated data to generate a library in order to identify real-time damage mechanisms. Fig. 1: (a) Amplitude and roll-off frequency vs. source/sensor distance for experimental signals and numerical signals. (b)Evolution of Partial Power PP1 [0–125 kHz] as a function of amplitude obtained with a nano 30 sensor for several sources. Fiber break and debonding (L = 20 μm or 100 μm). EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

    

   

Textile Reinforced Cementitious (TRC) sandwich composites provide a load-bearing, noncorrosive, lightweight, and durable alternative for steel-reinforced sandwich elements, and/or traditional steel-reinforced concrete. However, the composite nature of the material and slender nature of the facings render the fracture behavior complex. Insufficient interlaminar bond can cause premature debonding, substantially reducing the loadbearing capacity of the composite. Non-Destructive Testing (NDT) techniques seem the obvious choice to monitor the damage progression of the material without affecting, nor compromising the behavior of the composite, and predict their service life. In this study, TRC sandwich composites, subjected to quasistatic four-point bending, are monitored with three NDTs. Digital Image Correlation (DIC) allows to measure the surface strains and displacements. MMW Spectrometry, used for the first time in bending damage monitoring, allowed to detect damage such as cracking, or debonding, while Acoustic Emission (AE) allowed to localize and characterize internal cracking. In order to simulate premature debonding, the bond between the tensile TRC facing and the insulation, in the central zone, where the bending moment is maximum, was artificially destroyed. Results show that a weak interlaminar bond reduced the ultimate load of the composite by more than 50%. Additionally, DIC, AE and MMW Spectrometry proved useful to monitor and characterize damage. Multimodal data gathered from the multimodal NDTs showed to be complementary. DIC allowed to interpret AE and MMW Spectrometry data from a surface viewpoint, while AE parameters permit predictions at low load conditions, and detect internal cracking. For instance, the AE behavior at early load stage (less than 15% of the maximum load) of the TRC sandwich with destroyed bond showed significant differences than for the reference TRC sandwich. Specifically, it showed higher RA values, and lower AF than the reference TRC sandwich, suggesting more shear related early activity for, promoted by the damaged bond. Results were corroborated with DIC, while MMW Spectrometry seemed to follow closely the level of damage of TRC sandwich composites under quasi-static four-point bending. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

    

   

This work focuses on the numerical simulation of the AE due to transverse cracking in laminate composites. The objective of the work is the experimental characterization and numerical simulation of the influence of the ply thickness and stacking sequence on transverse matrix cracking induced acoustic emission. AE signals induced by transverse matrix cracking are simulated numerically using finite elements (FE) for composite laminates exhibiting different number of plies and stacking sequences. 3D FE models of the specimens are set-up using Abaqus™ Standard. Either [0n/90n/0n] or [90n/0n/90n] (n=1 or 3) composite laminates are modeled, one ply thickness is 0.3 mm. Matrix transverse cracking in 90 deg. inner or outer ply is simulated. The influence of the ply thickness on acoustic emission signals recorded at the crack epicenter is significative only for inner ply transverse cracking, whereas similar signals are obtained for outer ply cracking. The frequency content of signals induced by outer ply transverse cracking does not depend on the ply thickness. Contrary to outer ply cracking, the influence of the ply thickness on inner ply transverse cracking induced signals is significative, especially on the frequency content, and on the frequency centroid only close to the crack (Fig. 1). Outer ply cracking rather exhibits signals with a low frequency content, not depending much on the ply thickness, contrary to inner ply cracking, for which the frequency content is higher and more dependent on the ply thickness. Fig.1: Frequency centroid as a function of distance between the source and the sensor obtained numerically for [0n/90 n/0n] and [90n/0n/90n] stacking sequences (n=1 or 3). Results obtained without sensor effect, with a virtual perfect sensor. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

    

   

During plastic deformation of crystalline materials, a soft plasticity, made of numerous uncorrelated dislocation movements coexists with a wilder plasticity, in the form of collaborative movements: dislocation avalanches. The coexistence of the two plasticities depends on the establishment of a dislocation structure, which is supposed to hinder the propagation of avalanches. We propose to study the correlation between the microstructural evolution of the dislocation arrangements and the nature of the dislocation dynamics, during cyclic loading of pure copper single crystals. Different fatigue tests with imposed stress amplitude are performed to study the influence of (i) the loading path, (ii) the loading ratio and (iii) the crystallographic orientation on the plasticity phenomena. The acoustic emission (AE) technique is used to study both types of plasticity : the continuous AE is associated with soft plasticity and the discrete AE with wild plasticity. The dislocation microstructures are studied using EBSD (crystal disorientation) and ECCI (Electron Channeling Contrast Imaging) techniques at the end of each fatigue stage. The AE-ECCI coupling gives valuable information about the dislocation dynamics of dislocations. This study shows a certain universality, with (i) the existence of dislocation avalanches, produced during a more or less deep reorganization of the structures, (ii) a progressive evolution, during the cycles, of the dislocation mean free path, associated with the emergence of a dislocation structure and (iii) an inhibition of avalanches during the emergence of a dislocation arrangement. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

    

   

French Projects of Investment for the Future, called “Research for Nuclear Safety and Radiation Protection” have been initiated to further research on the causes, the management, the impact of the observed nuclear accidents and to propose and validate solutions to limit the risk and the consequences. In this context the "Non Destructive Evaluation of nuclear plants containment” project” (ENDE) with eight partners (six research institutes and two industrials) supported by the “National Agency of Research”, proposes a methodology for the Non Destructive Evaluation of the containment capacity. The two major functions to be assess are strength and leak tightness. Under the frame of the VeRCoRs project EDF has developed and build a containment mock-up on the 1/3 scale (diameter 20m, height 20m, wall thickness 40cm) which has been used for some partners of ENDE project. Mistras has been involved in characterisation of concrete cracking during pneumatic proof tests either in ENDE and VeRCoRs programs. Since some leaks occurs in the area of monitoring we use AE to characterized them. The mockup has been used to develop and characterized an instrumentation and technology for leak detection with a major challenge leak detection has to be performed from this inside of the containment building with all the contingences of operating of full scale operating nuclear plant. This paper describe the steps of development and validation of the methodology up to the application this measurement on site help the leak characterisation during pneumatic ten year Integrated Leakage Rate Test at 4,2 bar. EWGAE 35, Ljubljana, Slovenia, 13th – 16th Sep. www.ewg

    

   

Carbon Fiber Reinforced Polymer (CFRP) composites are broadly used in engineering applications. Their inherent anisotropy due to different fiber orientations can be considered an advantage since the strength of the component can be designated in preferential loading directions. However, this anisotropy leads to multiaxial stress conditions, complicating their damage sequence and mechanical response. Identification of these multiaxial conditions at early loading stages is of paramount importance to predict the upcoming structural response of the material. Acoustic Emission (AE) is applied in this study to CFRP laminates with different stacking sequences, in which different multiaxial conditions are generated. Laminates consisting of 30o plies are characterized by dominant shear stresses, whereas in laminates with 60o layers transverse normal stresses govern the stress state. Through quasi-static and incremental loading, it is shown that certain AE features can be used to identify the dominant stress component rather than just the occurring damage mode even at early loads, before severe fracture influences the mechanical capacity. This is of great importance in cases that detrimental shear stresses are generated, leading to delaminations and mechanical deterioration. AE can be used in this direction to predict the upcoming damage and to take necessary measures to avoid final failure.

    

   

Engineered wood product (EWP) offers an improvement in performance and mechanical properties over the use of sawn timber. This is mainly due to the fact that these products can eliminate defects such as knots, splits, etc. The removal of these defects has been achieved through the development of the finger-joint technique. This technique makes it possible to merge boards together to produce the desired length or width, making it possible to manufacture, among other products, laminated beams of larger dimensions. Therefore, the evaluation of these joints in a laminated element is vital to ensure a quality final product, as they become the areas with the highest stress concentration. To this end, this work aims to carry out an evaluation of the mechanical behaviour of elements with and without finger-joints made of poplar monitored with acoustic emission and DIC, as well as to obtain parameters to predict the failure in the specimens with finger-joints.

    

   

Acoustic emission monitoring took place in a long-term test in a coal fired power plant in Germany for 4 years. The test object was a steel pipe with a ceramic matrix composite (CMC) jacket, which was installed in a bypass of a live steam line. The peak operating temperature was approx. 530 °C. The aim of the AE monitoring was to investigate damage evolution in the CMC jacket. The test pipe was removed from the power plant in 2021. Due to several reasons, the jacket did not experience high loads during operation and therefore information about damage mechanisms in the AE data is rare. However, a lot could be learned from this project concerning long term stability of the equipment in rough environment, data storage and filtering and about sensor long term coupling of AE sensors at high temperatures. The high temperature AE sensors were applied directly onto the surface of the steel pipe and the CMC jacket using a ceramic glue. Additionally, the sensors were held by stainless steel bands which were acoustically decoupled by mineral wool. The application of the sensors took place at a temperature of about 30 °C. It was not possible to check on the quality of the coupling during operation as the whole pipe was covered by insulation, including all sensors. Also, the sensors did not allow pulsing as test for the coupling quality. Effects like thermal expansion of sensors, CMC jacket and ceramic glue had to be considered. Additionally, the power plant adepts its electrical output to the demands by flexible operation. This leads to cyclic changes in temperature and a high amount of heating and cooling cycles, which affects the coupling condition of the AE sensors. During dismantling of the test pipe from the power plant, a visual inspection of the sensor coupling was possible. The condition of the sensor coupling was documented before and after the sensors were removed. Pencil lead breaks were performed to quantify the quality of coupling as well. It could be shown that long term coupling of AE sensors is possible even in high temperature environment combined with cyclic temperature changes.

    

   

This paper summarizes a Final Draft International Standard (FDIS) developed by ISO TC 135 SC 9 WG 9. Since the draft comprises 60 pages, only an overview can be presented in this compressed format.

    

   

This paper discusses an example of practical implementation of Acoustic Emission continuous monitoring in the context of the Fourth Industrial Revolution and the new NDE4.0 paradigm, on renewable electric power wind farms. This project incorporates new sensors, a remote-wireless smart AE instrument, cloud data analytics tailored for data fusion, automatic analysis, alarming, and a data-driven web application for the visualization of asset status in real- or close to realtime. This example clearly illustrates the roll of AE as a natural method for NDE4.0 realization at the beginning of the third decade of the 21st century.

    

   

The paper presents a case study of a considerably cracked and degraded bridge in Slovenia: with the implementation of in-situ measurements under bending and shear and the use of a nondestructive acoustic emission technique. Despite the existing crack system, the latter was able to detect microstructural changes. These were characterised by low values of average frequency (AF), as well as lower values of the rise time-amplitude ratio (RA), and energy. A correlation between shear capacity and acoustic activity was observed. This promises to expand the use of AE in the process of assessing of the load-bearing capacity of existing concrete structures.

    

   

As existing concrete structures age, several degradation phenomena can endanger their structural safety. A severe threat to the integrity of concrete is posed by the alkali-silica reaction, which starts internally by the formation and swelling of a hydrophilic gel and eventually leads to concrete cracking. The acoustic emission technique can be applied to monitor ongoing damage caused by degradation processes. However, due to the working principle of the technique, only active damage can be detected. This paper investigates damage activation protocols to assess already existing damage in a limited timeframe. Small concrete samples that were deteriorated up to a target damage level in an accelerated way are investigated. Several activation protocols such as changing the moisture content, applying temperature fluctuations, and heating the samples with a heat lamp are applied and analyzed. It is found that changing the moisture content is most promising in terms of AE activation, its ability to distinguish damaged and undamaged samples, and allow damage localization.

    

   

This study focuses on the potential of Textile Reinforced Cementitious (TRC) composites with alkali-resistant glass textile to reinforce masonry structures. In particular, a better identification of the debonding mechanisms is a crucial point for a more efficient use of these composites. Twelve single-lap shear bond tests are performed to investigate four strengthening configurations - two matrices and two reinforcement ratios. This paper discusses the applicability of acoustic emission to assess the damage state of TRC during adherence testing. The flexibility of the matrix used and the amount of reinforcement of the TRC affect the cumulative amplitude distributions. The accumulation of the partial frequency associated with high frequency (above 400 kHz) is a precursor of a strong contribution of the textile in the load transfer.

    

   

This paper analyzes the theoretical basis of acoustic emission monitoring of leakage in principle. Based on the actual field leakage experiments, the following quantitative relationships are obtained: the quantitative relationship between the amount of leakage and the acoustic emission parameters under the same pressure; the quantitative relationship between different pressures, acoustic emission parameters and leakage rate under the condition of the same valve opening; the characteristic relationship between different leakage openings and acoustic emission parameters under the same pressure difference (tank wall plug). An online experimental demonstration system of leakage rate of water pipes is established. The acoustic emission collector automatically detects the leakage and leakage rates, and transmits the data to the cloud server. After the alarm conditions are set, the alarms will be pushed to the mobile phone if the alarm conditions are met. The cloud server is open for readers to view the results.

    

   

Localized corrosion is one of the most dangerous damages that can occur on metals, affecting the structure/component integrity. The early detection of such corrosion type is challenging for field applications, especially if a coted metal is used (e.g. coated aluminum alloys used in the aeronautical industry). In the present study the use of the Acoustic Emission technique (AE) is proposed to monitor the evolution of the localized corrosion, from the initial pitting that evolves to intergranular corrosion (IGC) prior to the material exfoliation (EFC). Coated (anaphoretic ecoating) aluminum alloy 2024-T3 coupons were exposed to the EXCO solution (ASTM G34) for different time spans, and characterized by optical microscopy to evaluate the degradation. The most relevant parameters that characterize the AE signals were identified, allowing to classify practically all intervals of activity (≈80-90%) into 4 well-differentiated classes. The time distribution of such classes is in good agreement with the different stages (mechanisms) of the corrosion process as identified by the microstructural characterization. The AE data analysis has revealed the promising potential of this technique to distinguish between the different steps of the corrosion process, and pave the way to the detection of localized corrosion on coated aluminum alloys.