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1
Mathiyaparanam, Jeyisanker. "Analysis of acoustic emission in cohesionless soil." [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001715.
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Elfergani, Hisham. "Acoustic emission analysis of prestressed concrete structures." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/49383/.
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This thesis examines the role of Acoustic Emission (AE) as a non-destructive testing (NDT) technique for prestressed and reinforced concrete structures. The work focuses on the development of experimental techniques and data analysis methods for the detection, location and assessment of AE from prestressed and reinforced concrete specimens. This thesis reveals that AE can be used to detect the onset of corrosion activity in wire in the interface between prestressed concrete and mortar as found in prestressed concrete pipes. Furthermore, this technique can be used to locate the corrosion activity on different size prestressed concrete samples. By correlation between three parameters of classical AE analysis techniques (traditional parameters), damage can be detected and located whilst the corrosion area, macro crack and crack propagation can be identified. However, it cannot classify the crack type. Different damage modes, including corrosion activity, micro/macro cracking formation, crack propagation and wire failure generate different types of AE signals with varying amplitudes and absolute energy emitted. A novel analysis approach has been used on composite materials (concrete, mortar and steel) to evaluate differing crack types by a combination of the classical acoustic emission analysis technique and advanced analysis Rise time / Amplitude (RA) and Average Frequency (AF), results proved the effectiveness of the developed techniques for damage detection and classification crack types. The relationship between RA value and AF value can be used to determine the crack area and classify it as either tensile crack type, other type (shear movement) or no crack. The results of the research have demonstrated that the AE technique is valid in larger scale monitoring and hence the potential for monitoring real structures such as prestressed concrete pipes. Use of Kernel Density Estimation Function (KDEF) provides improved visualisation of the data to represent clearly the RA/AF values. Key Words: Acoustic Emission, Corrosion, Reinforced Concrete, Prestressed Concrete, Micro and Macro Concrete Cracks, Crack classification, Source Location, Damage Assessment, Monitoring.
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Miller, D. G. "Acoustic emission analysis of an automotive paint system." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/47293.
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Mirhadizadeh, S. A. "Monitoring hydrodynamic bearings with acoustic emission and vibration analysis." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/7888.
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Acoustic emission (AE) is one of many available technologies for condition
health monitoring and diagnosis of rotating machines such as bearings. In
recent years there have been many developments in the use of Acoustic
Emission technology (AET) and its analysis for monitoring the condition of
rotating machinery whilst in operation, particularly on high speed machinery.
Unlike conventional technologies such as oil analysis, motor current signature
analysis (MCSA) and vibration analysis, AET has been introduced due to its
increased sensitivity in detecting the earliest stages of loss of mechanical
integrity.
This research presents an experimental investigation that is aimed at
developing a mathematical model and experimentally validating the influence of
operational variables such as film thickness, rotational speed, load, power loss,
and shear stress for variations of load and speed conditions, on generation of
acoustic emission in a hydrodynamic bearing. It is concluded that the power
losses of the bearing are directly correlated with acoustic emission levels. With
exponential law, an equation is proposed to predict power losses with
reasonable accuracy from an AE signal.
This experimental investigation conducted a comparative study between AE
and Vibration to diagnose the rubbing at high rotational speeds in the
hydrodynamic bearing. As it is the first known attempt in rotating machines. It
has been concluded, that AE parameters such as amplitude, can perform as a
reliable and sensitive tool for the early detection of rubbing between surfaces of
a hydrodynamic bearing and high speed shaft.
The application of vibration (PeakVue) analysis was introduced and compared
with demodulation. The results observed from the demodulation and PeakVue
techniques were similar in the rubbing simulation test. In fact, some defects on
hydrodynamic bearings would not have been seen in a timely manner without
the PeakVue analysis.In addition, the application of advanced signal processing and statistical
methods was established to extract useful diagnostic features from the acquired
AE signals in both time and frequency domain. It was also concluded that the
use of different signal processing methods is often necessary to achieve
meaningful diagnostic information from the signals. The outcome would largely
contribute to the development of effective intelligent condition monitoring
systems which can significantly reduce the cost of plant maintenance.
To implement these main objectives, the Sutton test rig was modified to assess
the capability of AET and vibration analysis as an effective tool for the detection
of incipient defects within high speed machine components (e.g. shafts and
hydrodynamic bearings).
The first chapter of this thesis is an introduction to this research and briefly
explains motivation and the theoretical background supporting this research.
The second and third chapters, summarise the relevant literature to establish
the current level of knowledge of hydrodynamic bearings and acoustic emission,
respectively. Chapter 4 describes methodologies and the experimental
arrangements utilized for this investigation. Chapter 5 discusses different NDT
diagnosis. Chapter 6 reports on an experimental investigation applied to
validate the relationship between AET on operational rotating machines, such
as film thickness, speed, load, power loss, and shear stress. Chapter 7 details
an investigation which compares the applicability of AE and vibration
technologies in monitoring a rubbing simulation on a hydrodynamic bearing.
5
Evans, Mark Julian. "The use of diffuse field measurements for acoustic emission." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267787.
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Moghisi, M. "Ultrasonic and acoustic emission studies of plasma sprayed coatings." Thesis, University of Bath, 1985. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332455.
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This work assesses the potentials of two NDE techniques namely ultrasonic C-scan and acoustic emission for evaluating plasma sprayed coating quality. The coating materials used were aluminium (Metco 54), alumina (Metco 105), molybdenum (Mob3) and self-fusing molybdenum (Mo5O5). It has been established that ultrasonic C-scan imaging can reliably detect thickness variations of the order of 0.05mm in plasma sprayed coatings. Also, by using this technique it is possible to detect the presence of delamination or lack of adhesion between the coating and substrate. Although it was only possible to produce aluminium and alumina coatings with artificially introduced adhesion defects, it has been shown that the presence of such defects in other coatings can also be detected. It has been established that an ultrasonic C-scan technique is not sensitive to the process parameters of plasma spraying. The process parameters investigated were; poor surface preparation, input power and surface cooling. Another major limitation of ultrasonic C-scan technique is the geometrical restrictions where components with high curvatures can not be tested. Acoustic emission activities from plasma sprayed coatings were monitored during four point bend testing. Samples sprayed on poorly prepared surfaces or sprayed without coolant air could be distinguished from control samples using AE characteristics at low strain levels. Also the AE response of the alumina coatings reflected the thickness of the coatings. Thicker coatings produced more AE events. The AE response of the molybdenum (Mo63) and self-fusing molybdenum (Mo5O5) coatings were complex. It was found that they were related to the residual stresses in the coatings. Aluminium coatings showed very little acoustic emission activities.
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Shum, Pak W. "A critical analysis of the acoustic emmission technique for NDE of pressure vessels." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-09192009-040341/.
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Faisal, Nadimul Haque. "Acoustic emission analysis for quality assessment of thermally sprayed coatings." Thesis, Heriot-Watt University, 2009. http://hdl.handle.net/10399/2295.
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This study describes a new approach to the quality assessment of thermally sprayed carbide and ceramic coatings produced by High Velocity Oxy-Fuel (HVOF) and Air Plasma Spray (APS) processes. The aim of the work was to develop an experimental methodology based on Acoustic Emission (AE) monitoring of a dead-weight Vickers indentation to assess the degree of cracking and hence the toughness of the coating. AE monitoring was also applied to an industrial process as a contribution to the possibility of quality assessment during the deposition process. AE data were acquired during indentation tests on samples of coating of nominal thickness 250-325 μm at a variety of indentation loads ranging from 49 to 490 N. Measurements were carried out on six different thick-film coatings (as-sprayed HVOFJP5000/ JetKote WC-12%Co, HIPed HVOF-JetKote WC-12%Co, as-sprayed HVOFJP5000 WC-10%Co-4%Cr, conventional powder APS-Metco/9MB Al2O3 and fine powder HVOF-theta gun Al2O3) and also on soft and hard metallic samples and metals. The raw AE signals were analysed along with force and displacement history and the total surface crack length around the indent determined. Also, a selection of the indents was sectioned in order to make some observations on the sub-surface damage. The results show characteristic AE time evolutions during indentation for tough metals, hard metals, and carbide and ceramic coatings. Within each category, AE can be used as a suitable surrogate for crack length measurement for assessing coating quality. Finally, a preliminary observation on AE monitoring during HVOF (JP5000) WC- 10%Co-4%Cr thermal spraying was made. It was found that AE is sensitive to individual particle landings during thermal spraying and therefore can, in principle, be used to monitor the spray process.
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Flannigan, James Christopher. "Acoustic emission monitoring of fiber reinforced bridge panels." Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/890.
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Elghamry, Mohamed Hussein. "Performance and condition monitoring of reciprocating machines using acoustic emission." Thesis, Heriot-Watt University, 2000. http://hdl.handle.net/10399/1125.
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Sibbald, David Bruce. "Development of data acquisition and analysis methods for chemical acoustic emission." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/28829.
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Acoustic Emission Analysis (AEA) is the study of the sonic (and ultrasonic) energy released by chemical systems in the form of transient waves, as the system attempts to (re)attain equilibrium. This area of chemistry, and chemical analysis, is ripe for fundamental studies since it has been little explored. The high potential of the technique as a non-invasive, non-destructive reaction monitoring scheme suggests that numerous applications will follow.
In this work, an apparatus and software have been constructed to monitor acoustic emission (AE) and collect and process AE data. A broad-band piezoelectric transducer was used to convert the acoustic signals to electrical waveforms which could be captured by a digital storage oscilloscope. These waveforms were then stored on an IBM-compatible computer for further analysis.
Analysis of the data was performed using pattern recognition techniques. The signals were characterized through the use of descriptors which can map each signal onto a multi-dimensional feature space. Visualization of the data structure in multidimensional
space was accomplished using several methods. Hierarchical clustering was used to produce tree structures, known as dendrograms, which attempt to show clustering of the signals into various groups. Abstract factor analysis (AFA) - also called principal components analysis (PCA) - was used to project the data onto a two dimensional factor space to allow for direct viewing of structure in the multidimensional
data.
Sodium hydroxide dissolution, aluminum chloride hydration and heat activation of Intumescent Flame Retardants (IFR's) were used to test the assembled hardware and to provide data to submit to the pattern recognition algorithms coded as part of this
work. The solid-solid phase transition of trimethylolethane (Trimet), and the liquid crystal phase transitions of two liquid crystals (α-ѡ-bis(4-n-decylaniline-benzilidene-4'-oxyhexane), and 4-n-pentyloxybenzylidene-4'-n-heptylaniline) were also monitored and the signals analyzed.
The pattern recognition software was able to extract much information from the acoustically emitting samples - information which would not have been apparent by using standard (uni- and bi-variate) methods of analysis. Chemical acoustic emission, coupled with pattern recognition analysis, will be able to provide the chemist with knowledge (qualitative, quantitative, kinetic, etc.) about chemical systems which are often difficult or impossible to monitor and analyze by other means.Science, Faculty of
Chemistry, Department of
Graduate
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Aljets, Dirk. "Acoustic emission source location in composite aircraft structures using modal analysis." Thesis, University of South Wales, 2011. https://pure.southwales.ac.uk/en/studentthesis/acoustic-emission-source-location-in-composite-aircraft-structures-using-modal-analysis(6871e94b-6e94-4efd-b563-41b254ee27b4).html.
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The aim of this research work was to develop an Acoustic Emission (AE) source location method suitable for Structural Health Monitoring (SHM) of composite aircraft structures. Therefore useful key signal features and sensor configurations were identified and the proposed method was validated using both artificially generated AE as well as actual AE resulting from damage. Acoustic Emission is a phenomenon where waves are generated in stressed materials. These waves travel through the material and can be detected with suitable sensors on the surface of the structure. These stress waves are attributed to propagating damage inside the material and can be monitored while the structure is in service. This makes AE very suitable for SHM, in particular for aircraft structures. In recent years composite materials such as carbon fibre reinforced epoxy (CFRP) are increasingly being used for primary and secondary structures in aircraft. The anisotropic layup of CFRP can lead to different failure mechanisms such as delamination, matrix cracking or fibre breakage which affects the remaining life time of the structure to different extents. Accurate damage location is important for SHM systems to avoid further inspections and allows for a maintenance scheme which considers the severity of the damage, due to damage type, extent and location. This thesis presents a novel source location method which uses a small triangular AE sensor array. The method determines the origin of an AE wave by a combination of time of arrival and modal analysis. The small footprint of the array allows for a fast and easy installation in hard-to-reach areas. The possibility to locate damage outside and at a relatively far distance from the array could potentially reduce the overall number of sensors needed to monitor a structure. Important wave characteristics and wave propagation in particular in CFRP were investigated using AE simulated by an artificial source and actual damage in composite specimens.
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Locey, Lance Lester. "Analysis and Comparison of Three Acoustic Energy Density Probes." Diss., CLICK HERE for online access, 2004. http://contentdm.lib.byu.edu/ETD/image/etd561.pdf.
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Beck, Paul. "Quantitative damage assessment of concrete structures using Acoustic Emission." Thesis, Cardiff University, 2004. http://orca.cf.ac.uk/54656/.
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This thesis examines the role of Acoustic Emission (AE) as a non-destructive testing technique for concrete structures. The work focuses on the development of experimental techniques and data analysis methods for the detection, location and assessment of AE from the failure of plain and reinforced concrete specimens. Four key topics are investigated:
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Alshimmeri, Fiasael. "Diagnosis of low-speed bearing degradation using acoustic emission techniques." Thesis, Cranfield University, 2017. http://dspace.lib.cranfield.ac.uk/handle/1826/12324.
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It is widely acknowledged that bearing failures are the primary reason for
breakdowns in rotating machinery. These failures are extremely costly,
particularly in terms of lost production. Roller bearings are widely used in
industrial machinery and need to be maintained in good condition to ensure the
continuing efficiency, effectiveness, and profitability of the production process.
The research presented here is an investigation of the use of acoustic emission
(AE) to monitor bearing conditions at low speeds.
Many machines, particularly large, expensive machines operate at speeds below
100 rpm, and such machines are important to the industry. However, the
overwhelming proportion of studies have investigated the use of AE techniques
for condition monitoring of higher-speed machines (typically several hundred
rpm, or even higher). Few researchers have investigated the application of these
techniques to low-speed machines (<100 rpm), This PhD addressed this
omission and has established which, of the available, AE techniques are suitable
for the detection of incipient faults and measurement of fault growth in low-speed
bearings.
The first objective of this research program was to assess the applicability of AE
techniques to monitor low-speed bearings. It was found that the measured
statistical parameters successfully monitored bearing conditions at low speeds
(10-100 rpm).
The second objective was to identify which commonly used statistical parameters
derived from the AE signal (RMS, kurtosis, amplitude and counts) could identify
the onset of a fault in either race. It was found that the change in AE amplitude
and AE RMS could identify the presence of a small fault seeded into either the
inner or the outer races. However, the severe attenuation of the signal from the
inner race meant that, while AE amplitude and RMS could readily identify the
incipient fault, kurtosis and the AE counts could not. Thus, more attention needs
to be given to analysing the signal from the inner race. The third objective was to identify a measure that would assess the degree of
severity of the fault. However, once the defect was established, it was found that
of the parameters used only AE RMS was sensitive to defect size.
The fourth objective was to assess whether the AE signal is able to detect defects
located at either the centre or edge of the outer race of a bearing rotating at low
speeds. It is found that all the measured AE parameters had higher values when
the defect was seeded in the middle of the outer race, possibly due to the shorter
path traversed by the signal between source and sensor which gave a lower
attenuation than when the defect was on the edge of the outer race. Moreover,
AE can detect the defect at both locations, which confirmed the applicability of
the AE to monitor the defects at any location on the outer race.
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Hollis, Gaylon C. "Non-Invasive Acoustic Emission Testing of Compressed Trabecular Bone and Porous Ceramics using Seismic Analysis Techniques." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4816.
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Acoustic emission(AE) is one of the most sensitive techniques to non invasively monitor deformation, fatigue, and fracture of many materials. The purpose of this study was to evaluate the potential to use AE to detect local failure events within porous ceramic materials. The primary material of interest was mineralized trabecular bone. A better understanding of the failure of trabecular bone is highly relevant to skeletal fragility diseases such as osteoporosis.
This study sought to develop a post processing technique that could strengthen the relation between the events detected and the phenomena occurring as a specimen is loaded. The deficiency in other techniques is that they did not fully make a quantitative correlation between acoustic emission event characteristics and the physical occurrence of damage events. The study evaluated the use of seismic power laws because these laws were able to attach a quantitative model to an earthquake and its successive aftershocks. Earthquake transmission has similar propagation attributes when compared to acoustic emission; seismic waves radiate from the epicenter of an earthquake. Acoustic waves radiate from the source of energy release in an acoustic emission event.
The study measured the acoustic emission response of trabecular bone and highly oriented ceramics. The bone and ceramics were extracted in two perpendicular directions so that the structural orientation was different. The study sought to evaluate if the power-laws could differentiate the acoustic emission response based on varying the material and varying the structural orientation. The samples were quasi-statically compressed; the mechanical and acoustic emission data were simultaneously recorded.
The study found that using the seismic power-law did not statistically differentiate the directional orientation for trabecular bone or ceramic specimens. Acoustic emission did indicate that event detection was different for each type of the of material. Correlations were established with the acoustic emission response and the mechanical testing data. These relationships were explainable because of the mechanical properties of the material.
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Johnson, Mikael. "Acoustic Emission in Composite Laminates - Numerical Simulations and Experimental Characterization." Doctoral thesis, KTH, Solid Mechanics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3452.
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Zou, Daihu. "Numerical analysis of rock failure and laboratory study of the related acoustic emission." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/29226.
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Sudden rock failure in the form of rockbursting has long been a problem in underground mines. The basic mechanism of this phenomenon is still unresolved. This thesis describes the research work on this problem conducted by the doctoral candidate Daihua Zou in the Department of Mining and Mineral Process Engineering at The University of British Columbia, under the supervision of Professor Hamish D.S. Miller.
This research project was undertaken in order to investigate the process of violent rock failure and was achieved by examining various aspects of the rock failure mechanism.
The assumption that acoustic emission can be used as a reliable means of predicting rock failure was investigated, as well as the possibility that violent rock failure could occur in any mine rock.
As part of the research, a rock failure mechanism was postulated. A process analogous to shearing is postulated to be important at the post-failure stage. The stick-slip phenomenon has been analyzed using a numerical model under a variety of conditions. The conditions which could give rise to possible violent rock failure were determined. At the same time, acoustic emissions were tested from rock specimens under different loading conditions. The experimental results obtained show a correlation with field measurements made in a mine. In order to verify the testing results from limited experiments, a numerical acoustic model was developed, which is unique in that it is entirely based on the stick-slip process not on any acoustic theory. This model allows rock tests and their associated acoustic emission to be realistically simulated. With this model, acoustic emissions were simulated under various loading conditions for different kinds of rocks. The case of a hard or a soft intercalation was also modelled.Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate
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Facciotto, Nicolò. "Source differentiation and identification of acoustic emission signals by time-frequency analysis." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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In the context of Structural Health Monitoring, the Acoustic Emission Technique may be efficiently used to detect damage on aerospace structures. This study focuses on the development of a source identification algorithm to distinguish different acoustic emission events in aluminium sheets, which have been collected during experimental tests. The future goal will be the design of a Holistic Structural Health Monitoring System which will make the complete aircraft an intelligent structure able to diagnose its own structural damage based on the condition of the structure while maintaining safety.
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Dudko, Yuriy V. 1963. "Analysis of seismo-acoustic emission from ice fracturing events during SIMI'94." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/79978.
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Spasova, Lyubka Miroslavova. "Feasibility of acoustic emission testing and analysis applied to materials encapsulating nuclear wastes." Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522360.
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Sison, Miguel Fernando G. "Analysis of acoustic emission waveforms from fatigue cracks on a steel bridge hanger." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-02132009-172406/.
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Sharma, Anuradha. "Frequency Based Study of Crack Analysis using Acoustic Emission in Polymer Matrix Composite." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron160742750648654.
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Kaza, Avinash. "Preparation of acoustic emission data for neural network analysis using AWK and C programs." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://etd.wvu.edu/etd/controller.jsp?moduleName=documentdata&jsp%5FetdId=3896.
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Thesis (M.S.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains xiv, 189 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 157-160).
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Allan, Pamela. "Studies in Raman, infrared and acoustic emission spectrometries and reaction calorimetry for process analysis." Thesis, University of Strathclyde, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501904.
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Chen, Heng-Hsueh. "Damage Detection of Carbon Fiber Reinforced Polymer Using Electrical Measurement and Analysis of Acoustic Emission Signals." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1383455687.
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Mohammed, Bizuayehu Y. "Damage characterisation in twill-weave CFRP composite aircraft structures using modal analysis of acoustic emission signals." Thesis, University of South Wales, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.702330.
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The aim of this research work is to propose a damage characterisation method using acoustic emission technology. The research is broadly categorised in structural health monitoring (SHM) of CFRP composite structures. A number of tests were performed on twill-weave CFRP composite material in correlating the various damage types to their associated signal features. Recent developments in aircraft structural material lead to an increase use of CFRP composite structures. However, these materials are susceptible to different modes of failures such as matrix cracking, delamination, stringer debonding, and fibre fracture which affect the integrity of the structure. Determining the type of failure during service life of an aircraft structure is an important input in the SHM of materials. This can potentially reduce inspection time, and increases knowledge of the damage type propagating within the said structure. Acoustic emission (AE) is a phenomenon where a stress wave is generated due to stresses in a material. AE sensors can be placed on the surface of the structure to detect these waves while the material is in service. These waves have possess distinct signal features which can be attributed to a particular damage type. Therefore, AE based technology is potentially suitable for the SHM of composite structures. This thesis proposes an improved damage characterisation method for twill weave CFRP composite when subjected to various modes of failure. These failure modes were achieved using a variety of test setups namely cantilever bending, three point bending, stringer debonding, and tensile testing. The proposed method uses live digital microscope video recording of events along with AE events. Distinct signal features were identified for delamination initiation and propagation, matrix cracking, fibre fracture and skin-stringer debonding.
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Filho, Marcos Daniel Gouveia. "Signal characteristics of acoustic emissions from the axial strain in polyethylene manhole." Universidade Federal do CearÃ, 2015. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=14471.
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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgicoThe use of new materials in the sanitation industry aims to improve water treatment conditions and optimize the performance of the structures of sewage systems. Studies show that investments in sanitation are four times more effective than health. Manhole (PV) is an integral structure of the collection networks of major importance sewage because it is the sewage flow of the meeting from various facilities that are guided and follow for further processing. Non-destructive tests are widely used in modern industry worldwide to evaluate the quality and detection of changes in structure, small surface flaws, presence of cracks and other physical disruptions, being capable of detecting flaws in structures prematurely allowing constant monitoring and real time frame. The technique of acoustic emission (AE) is effective both during subsequent tests the implementation of the structure, guaranteeing their structural integrity, and in the real-time monitoring of the frame subject to the usual charging service, while performing its function without need of interrupting. To properly investigate the structure is necessary to know how the defects are and their respective acoustic activity. In this study, the acoustic emission signals generated in polyethylene manholes by variable axial deformation during loading are characterized both in time domain and in the frequency domain creating the signature of the defect.
A utilizaÃÃo de novos materiais na indÃstria do saneamento, visa melhorar as condiÃÃes do tratamento de Ãgua e otimizar o desempenho das estruturas de redes coletoras de esgoto. Estudos comprovam que os investimentos realizados em saneamento bÃsico sÃo quatro vezes mais efetivos que na saÃde. PoÃo de visita (PV) à uma estrutura integrante das redes coletoras de esgotos de grande importÃncia, pois nele ocorre o encontro do fluxo de esgotos provenientes de diversas instalaÃÃes que sÃo orientados e seguem para o posterior tratamento. Os ensaios nÃo destrutivos sÃo largamente utilizados na indÃstria moderna em todo o mundo para avaliaÃÃo da qualidade e detecÃÃo de variaÃÃes na estrutura, pequenas falhas superficiais, presenÃa de trincas e outras interrupÃÃes fÃsicas, sendo capaz de detectar prematuramente falhas em estruturas permitindo a monitoraÃÃo constante da estrutura e em tempo real. A tÃcnica de emissÃo acÃstica (EA) à eficaz tanto na fase de testes subsequentes à implementaÃÃo da estrutura, garantindo sua integridade estrutural, quanto no monitoramento em tempo real d a estrutura sujeita a carregamento usual de serviÃo, enquanto desempenha sua funÃÃo, sem necessidade de interrupÃÃo. Para investigar corretamente a estrutura à necessÃrio conhecer como os defeitos se manifestam e sua respectiva atividade acÃstica. Neste trabalho, os sinais de emissÃo acÃstica gerados em poÃos de visita de polietileno por deformaÃÃo axial durante carregamento variÃvel sÃo caracterizados tanto no domÃnio do tempo quanto no domÃnio da frequÃncia criando a assinatura do defeito.
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Tsai, Shu-Jen Steven. "Power Transformer Partial Discharge (PD) Acoustic Signal Detection using Fiber Sensors and Wavelet Analysis, Modeling, and Simulation." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/35983.
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In this work, we first analyze the behavior of the acoustic wave from the theoretical point of view using a simplified 1-dimensional model. The model was developed based on the conservation of mass, the conservation of momentum, and the state equation; in addition, the fluid medium obeys Stokes assumption and it is homogeneous, adiabatic and isentropic. Experiment and simulation results show consistency to theoretical calculation.
The second part of this thesis focuses on the PD signal analysis from an on-site PD measurement of the in-house design fiber optic sensors (by Virginia Tech, Center for Photonics Technology). Several commercial piezoelectric transducers (PZTs) were also used to compare the measurement results. The signal analysis employs the application of wavelet-based denoising technique to remove the noises, which mainly came from vibration, EMI, and light sources, embedded in the PD signal. The denoising technique includes the discrete wavelet transform (DWT) decomposition, thresh-holding of wavelet coefficients, and signal recovery by inverse discrete wavelet transform. Several approaches were compared to determine the optimal mother wavelet. The threshold limits are selected to remove the maximum Gaussian noises for each level of wavelet coefficients. The results indicate that this method could extract the PD spike from the noisy measurement effectively. The frequency of the PD pulse is also analyzed; it is shown that the frequencies lie in the range of 70 kHz to 250 kHz. In addition, with the assumed acoustic wave propagation delay between PD source and sensors, it was found that all PD activities occur in the first and third quadrant in reference to the applied sinusoidal transformer voltage.Master of Science
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Pérez, Arroyo Carlos. "Large eddy simulations of a dual-stream jet with shockcells and noise emission analysis." Thesis, Toulouse, INPT, 2016. http://www.theses.fr/2016INPT0093/document.
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Cette thèse fait référence au bruit de choc généré par des jets sousdétendus simple ou en configuration co-axial. Le bruit de choc est généré par l'interaction entre les structures turbulentes de la couche de cisaillement et le réseaux de cellules de choc développé dans le cône potentiel du jet. Afin d'étudier le bruit choc, simulations à grandes échelles adaptés pour l'aéro-acoustique sont effectué avec des schémas d'ordre élevé qui permet une approche nondissipative et non-dispersive. Les résultats sont analysés et comparés avec des résultats expérimentaux. Notamment, une filtrage hydrodynamique et acoustique est réalisé dans le champ proche pour analyser les modes azimutaux acoustiques et hydrodynamiques. En outre, un analyse basé sur la transformé en ondelettes est mis en oeuvre pour identifier les caractéristiques acoustiques et hydrodynamiques importants des jets supersoniquesThis thesis deals with the shock-cell noise generated by under-expanded supersonic jets in single- and dualstream configurations. Shock-cell noise is generated by the interaction between the turbulent structures of the shear-layer and the shock-cell system developed in the potential core of the jet. In order to study shock-cell noise, large eddy simulations adapted to aeroacoustics are carried out using high-order compact schemes that allow for a non-dissipative nondispersive approach. The results are analyzed and compared to experimental results. In particular, an acoustic-hydrodynamic filtering is carried out in the near field in order to analyze the acoustic and hydrodynamic azimuthal modes. Moreover, a wavelet-based analysis is implemented in order to identify the relevant acoustic and hydrodynamic features of the supersonic jets
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Tesser, Juliano Accioly. "CaracterizaÃÃo de Defeitos de Soldagem por AnÃlise Fractal Utilizando EmissÃo AcÃstica em Ensaios de TraÃÃo." Universidade Federal do CearÃ, 2004. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=7329.
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O presente trabalho tem como objetivo caracterizar e correlacionar formas de onda de sinais de emissÃo acÃstica, utilizando mÃtodos de anÃlise espectral e fractal, em corpos de prova previamente soldados com seus respectivos defeitos, avaliando assim a integridade estrutural do material aÃo carbono ASTM 516 Grau 60, utilizado em vasos de pressÃo, tubulaÃÃes, esferas de armazenamento, etc. Os sinais de emissÃo acÃstica foram gerados submetendo os corpos de prova a ensaios de traÃÃo. Para anÃlise dos sinais no domÃnio dos tempos, foram utilizados o mÃtodo de contagem de caixas, que fornece a dimensÃo fractal, e o de intervalo re-escalado de Hurst, e no domÃnio das freqÃÃncias o mÃtodo espectral de Fourier. AtravÃs das relaÃÃes previstas pelas leis de escala, concluiu-se que os expoentes calculados pelos mÃtodos espectral de Fourier e reescalado de Hurst, correlacionam-se entre si, bem como com a dimensÃo fractal obtida pelo mÃtodo de contagem de caixas. Mostrou-se tambÃm a existÃncia de duas regiÃes de escala distintas que caracterizam a mudanÃa do regime elÃstico para o regime plÃstico quando as amostras foram submetidas ao carregamento de traÃÃo. Verificou-se ainda que este comporta-mento foi caracterÃstico tanto para os materiais soldados como para o metal de base.The present work aims to characterize and correlate waveforms of acoustic emission signals, using methods of spectral analysis and fractal in specimens previously soldiers with their defects, thus evaluating the structural integrity of the material carbon steel ASTM 516 Grade 60 used in pressure vessels, piping, storage spheres, etc.. The acoustic emission signals were generated by subjecting the specimens to tensile tests. For analysis of the signals in the time domain, we used the method of box counting, which provides the fractal dimension, and re-scaled range of Hurst, and in the frequency domain the Fourier spectral method. Through the relations laid down by law scale, it was concluded that the exponents calculated by Fourier transform and spectral methods reescalado Hurst, are correlated with each other as well as the fractal dimension obtained from a box counting. It was also shown existence of two regions of different scale characterizing the change of the elastic to the plastic regime when the samples were subjected to traction. It was further found that this behavior is characteristic for both the welded material as for the parent metal.
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Cao, Caihua. "Damage and Failure Analysis of Co-Cured Fiber-Reinforced Composite Joints." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/5298.
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Joints represent a design challenge, especially for composite structures. Among the available joining methods, co-curing is an efficient way to integrate parts for some applications. Coates and Armanios have proposed a Single Nested Overlap (SNO) co-cured joint configuration, obtained from a single lap joint through the overlap/interleafing of the adjoining top/bottom adherend plies, respectively. Through a comparative investigation, they have demonstrated joint strength and fatigue life improvements over the single lap joint counterparts for unidirectional and quasi-isotropic adherend lay-ups. This research extends the comparative investigation of Coates and Armanios by focusing upon characterizing and differentiating the damage initiation and progression mechanisms under quasi-static loading. Six specimen configurations are manufactured and tested. It is confirmed that single nested overlap joints show 29.2% and 27.4% average improvement in strength over single lap counterparts for zero-degree unidirectional and quasi-isotropic lay-ups, respectively.
Several nondestructive evaluation techniques are used to observe and analyze damage initiation, damage progression and failure modes of the studied specimens and to monitor their mechanical response. Using X-ray Radiography and Optical Microscopy techniques during quasi-static loading, a physical characterization of damage and failure mechanisms is obtained. The acoustic emission data acquired during monotonic loading could reveal the overall picture of AE activities produced by the damage initiation, development and accumulation mechanisms within the specimen via parametric analysis. Further AE analysis by a selected supervised clustering method is carried out and shown successful in differentiating and clustering the AE data. Correlation with physical observations from other techniques suggests that the resulting clusters may be associated to specific damage modes and failure mechanisms.
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Lopes, Wenderson Nascimento. "Investigação do conteúdo harmônico do sinal de emissão acústica na dressagem de rebolos de óxido de alumínio com dressador de ponta única." Universidade Estadual Paulista (UNESP), 2018. http://hdl.handle.net/11449/154406.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
A dressagem é uma operação muito importante para o processo de retificação. O objetivo desta é recondicionar o rebolo para restabelecer suas características de corte perdidas devido ao desgaste produzido após sucessivos passes. Sistemas de monitoramento que utilizam emissão acústica (EA) têm sido propostos para correlacionar os sinais com diversas condições da ferramenta. Este estudo traz uma nova abordagem de processamento de sinais de EA com o objetivo de identificar o momento correto para finalizar a dressagem, o que é essencial em um sistema de controle automático. A partir dos sinais de EA, coletados em testes de dressagem de rebolo de óxido de alumínio com dressador de ponta única, a análise espectral foi realizada por meio da Densidade Espectral de Potência (PSD, Power Spectral Density), selecionando-se bandas de frequências que melhor caracterizam o processo. O parâmetro estatístico "counts" foi aplicado ao sinal original não filtrado e filtrado nas bandas selecionadas para identificar a condição da ferramenta e, por sua vez, para a implementação de um sistema de monitoramento. Os resultados mostraram uma relação expressiva entre as condições de corte da ferramenta e os sinais processados nas bandas selecionadas. Houve uma grande diferença dos sinais filtrados nas bandas selecionadas e sinais não filtrados, refletindo que os filtrados foram mais eficientes em termos de automação de processos.
Dressing is an important operation for the grinding process. Its goal is to recondition the wheel tool to re-establish its cutting characteristics, owing to the wear produced after successive passes. Monitoring systems that use acoustic emission (AE) have been studied to correlate the signals with several tool conditions. This study brings a new approach of processing AE signals with the purpose of identifying the correct moment to stop the dressing, which is essential in an automatic control system. From the AE signals collected in dressing tests with aluminium oxide grinding wheel and single-point dresser, spectral analysis was made through power spectral density, selecting frequencies bands that best characterize the process. The statistical parameter ‘counts’ was applied to the raw signal unfiltered and filtered in the selected bands in order to identify the tool condition and, in turn, towards a monitoring system implementation. Results showed an expressive relation between tool cutting conditions and processed signals in the selected bands. There was a great disparity of the filtered signals in the selected bands and signals unfiltered, reflecting that the filtered ones were more efficient in terms of process automation.
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Alam, Akm Khorshed. "The detection of adhesive wear on cylinder liners for slow speed diesel engine through tribology, temperature, eddy current and acoustic emission measurement and analysis." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2599.
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The research concerns the condition monitoring of cylinder liner of large bore diesel engines using various methodologies to identify the onset of scuffing. The reasons of scuffing, improved designs and operational processes to prevent its occurrence were discussed. The research focused on modeling the normal condition of the cylinder liner with sufficient lubrication and detecting the precursor of scuffing by reducing the lubrication. The four detection systems used on the test facilities and field tests of the cylinder liners used tribology, temperature sensor, eddy current sensor and acoustic emission sensor. Experimental assessment of eddy current sensor was conducted for insufficient lubricating oil conditions for different cylinder liner wall pressures using a specially designed test facility. Field tests of temperature sensor and eddy current sensor were carried out on a 800mm bore worn cylinder liner of a container ship in service. Field test of acoustic emission sensor was carried out on a high speed automobile engine. Scuffing detection by temperature sensing should be considered as the last safety barrier, as it registers the after effect of scuffing and solely depends on the localized condition and the material’s thermal status. Mounting eddy current sensors are considered intrusive. Four sensors per cylinder are needed, which are prone to damage by the rings when the liner wears out. Additionally, the sensors measure only small section of the rings and their lubrication condition. Acoustic emission analysis effectively detects onset of scuffing on the cylinder liners and the rings. Initial findings from the lab and the field test on a four stroke engine confirmed this. However, more field tests under various loading condition on a slow speed engine is needed to understand the various event alignment and the non-routine detection, such as scuffing. They can be coupled with thermocouples to serve as a secondary protection.
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Simpson, Nathaniel Denis John. "An analysis of tensile strength, fracture initiation and propagation in anisotropic rock (gas shale) using Brazilian tests equipped with high speed video and acoustic emission." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for petroleumsteknologi og anvendt geofysikk, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-24284.
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This study attempts to further our knowledge of fracture behaviour by establishing an experimental system that links tensile strength, fracture initiation and propagation of an anisotropic rock (Mancos Shale) using an integrated Brazilian Test Setup equipped with Acoustic Emission and High Speed Video. The unique experimental conguration was applied to an anisotropic gas shale (Mancos Shale) in addition to other petroleum related reservoir rocks (such as sandstone and chalk). The variation in tensile strength, fracture initiation location, propagation time and the failure pattern are examined as a function between the layer plane and the loading direction. A time shift was shown to exist between the time at ultimate tensile stress and the time at fracture initiation. This phenomenon has been dubbed the Naet Shift.
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Aguiar, Juliano de. "CaracterizaÃÃo de Sinais de EmissÃo AcÃstica em Ensaios CTOD por AnÃlise Fractal." Universidade Federal do CearÃ, 2004. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=7343.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorA pesquisa teve como objetivo correlacionar diferentes defeitos e suas criticidades, em corpos de prova de aÃo ASTM A516 grau 60 para ensaio CTOD, cujos detalhes foram feitos no metal de base, no metal de solda e na zona termicamente afetada de uma junta soldada, com os sinais de emissÃo acÃstica obtidos durante os ensaios. Quatro mÃtodos de anÃlise fractal foram utilizados: anÃlise re-escalada de Hurst (R/S), dimensÃo de contagem de caixas, dimensÃo de cobetura mÃnima e anÃlise de flutuaÃÃo sem tendÃncias (DFA). Um nÃmero mÃnimo de pontos necessÃrios para a obtenÃÃo dos expoentes associados a cada mÃtodo de anÃlise foi determinado para os vÃrios sinais, bem como o efeito de diferentes mÃtodos de filtragem nesses expoentes. Verificou-se que nenhum dos mÃtodos isoladamente conseguiu caracterizar os defeitos nem os regimes de carregamento. Entretanto, utilizando-se representaÃÃes bidimensionais de todos os expoentes juntamente com o desvio padrÃo dos sinais foi possÃvel estabelecer, de forma satisfatÃria, uma caracterizaÃÃo hierÃrquica dos defeitos e regimes de carregamento.
The research aims to correlate different defects and their criticidades in specimens of ASTM A516 grade 60 CTOD test, details of which were made in the base metal in the weld metal and heat affected zone of welded joint with acoustic emission signals obtained during the tests. Four fractal analysis methods were applied: re-scaled analysis Hurst (R / S), the box counting dimension, cobetura minimum dimension and analysis of fluctuation without bias (DFA). A minimum number of points required to obtain the exponent associated with each method of analysis was determined for the various signals and the effect of different filtering methods such exponents. It was found that none of the methods alone failed to characterize or defects charging schemes. However, using two-dimensional representations of all the exponents with the standard deviation of signals could be made in a satisfactory way, a hierarchical characterization of defects and charging systems.
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Kelemen, Simon Gábor [Verfasser], and A. [Akademischer Betreuer] Albers. "Potentiale der Schallemissionsanalyse zur Charakterisierung von trockenlaufenden Friktionssystemen. Potentials of acoustic emission analysis for characterization of dry running friction systems / Simon Gábor Kelemen. Betreuer: A. Albers." Karlsruhe : KIT-Bibliothek, 2012. http://d-nb.info/1025887387/34.
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Marsh, Richard. "Experimental analysis of oil based cavitation peening in air." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43602.
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Oil Jet Cavitation Peening in Air (OPA) is capable of inducing compressive residual stress in standard aerospace materials. This paper demonstrates the process capabilities of OPA on Al 2024-T3. Specifically, changes in the workpiece residual stress, microhardness, mass loss and surface roughness are investigated as a function of the control parameters for the system. Additionally, the paper identifies a method to monitor the process in situ through the use of high frequency acoustic emission sensors. The results indicate the OPA process is capable of generating residual stresses comparable to those of standard shot peening, up to 60% of the yield strength of the material, at similar depths, around 300 µm. Finally, the acoustic emission signal may be utilized to monitor the process, specifically in predicting the microhardness and mass loss of the system.
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Al, Haj Omar. "Apports de l’émission acoustique couplée à la thermogravimétrie pour l’étude de la corrosion à haute température des métaux et alliages." Thesis, Saint-Etienne, EMSE, 2014. http://www.theses.fr/2014EMSE0765/document.
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La corrosion à haute température d'alliages métalliques représente un processus d’endommagement critique dans de nombreux domaines industriels. Le suivi en service de la dégradation des équipements opérant sous une atmosphère agressive à haute température devient un objectif majeur pour les industriels. Grâce à sa sensibilité et à son caractère non destructif, l'émission acoustique constitue une méthode intéressante pour suivre l’évolution de la détérioration des matériaux soumis à des formes sévères de corrosion comme le metal dusting pour les alliages de fer ou de nickel en pétrochimie. Notre étude a montré que les transformations irréversibles des matériaux telles que la fissuration peuvent être détectées grâce aux signaux acoustiques émis pendant la corrosion. Un couplage innovant a été développé associant l'émission acoustique in situ avec la thermogravimétrie. Dans un premier temps, ce couplage nous a permis d’étudier et d’approfondir nos connaissances de la corrosion à 900 °C sous atmosphère oxydante d’un alliage de zirconium. Les phénomènes comme la diffusion de l’oxygène dans la zircone ne sont pas émissifs ; par contre les mécanismes de dégradation irréversibles, comme l'initiation et la propagation des fissures dans la couche de zircone, sont décelables dès leur apparition. Dans un second temps, lors de l’étude de la carburation du fer pur ou du fer pré-Oxydé, nous avons démontré que la corrosion par metal dusting qui comporte une étape d’insertion des atomes de carbone dans la matrice de fer est détectable grâce à l’émission acoustique. Il est donc envisageable de suivre ce type de dégradation au moyen de l’émission acoustique lorsqu’il affecte les équipements industrielsHigh temperature corrosion of metallic alloys can cause damage to chemical and petrochemical industrial equipment. On line monitoring of the behaviour of components, which operate under corrosive atmosphere at high temperature, has become an important challenge. In order to quantify the level of damage of materials affected by corrosion, acoustic emission seems to be an interesting method due to its sensitivity and its non-Destructive aspect. Based on bibliographic supports, we have developed an experimental device combining thermogravimetric analysis with acoustic emission in order to simultaneously record the sample mass variations and the acoustic signals mainly due to the degradation of materials such as cracks formation during oxidation of metal at high temperature for example.First of all, we have studied Zircaloy-4 corrosion behavior at 900 °C under oxidant gas by means of this innovative equipment. We have demonstrated the feasibility of such a coupling method; mass measurements are not disrupted by acoustic emission chain connected to the thermobalance. Irreversible mechanisms, as cracks initiation and propagation, generate acoustic emission bursts. Analysis of the burst waveforms and of the oxidized sample cross sections allows us to attribute the acoustic events to corrosion or cooling processes. Secondary, metal dusting of pure iron at 650 °C under highly carburising gases (i-C4H10 + H2) was studied. Iron bulk degradation caused by graphite deposition and insertion has been detected using acoustic emission. This result lets us think that this technique can be adapted to monitoring of industrial equipment
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Schreier, Jan. "Vliv parametrů vazebného média a struktury povrchu na kvalitu snímaného signálu akustické emise." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-230124.
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This master’s thesis deals with the influence of different AE sensor couplants and surface roughness on the selected acoustic emission parameters. There are compared the amplitude of the signal measured using five different couplants at 20°C and 80°C. To monitor the effect of surface roughness on the AE parameters simple measuring product was constructed. Its functionality has been verified by implementation of basic experimental measurements.
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Monti, Arthur. "Élaboration et caractérisation mécanique d'une structure composite sandwiche à base de constituants naturels." Thesis, Le Mans, 2016. http://www.theses.fr/2016LEMA1023/document.
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Les éco-composites s'imposent progressivement comme une alternative à certains matériaux classiques. L'utilisation de fibres végétales en guise de renfort permet en effet d'améliorer les performances environnementales de ces matériaux ainsi que leurs propriétés spécifiques élevées. Dans ce contexte, cette étude propose d'élaborer un éco-composite sandwich dont les peaux sont constituées d'une résine thermoplastique innovante associée à des fibres de lin et à une âme en balsa. Tout d'abord, les comportements statiques de la résine et de l'âme sont analysés. Par la suite, le composite renforcé de fibres de lin constituant les peaux du sandwich est étudié. Les caractéristiques élastiques principales du pli UD en contraintes planes sont déterminées. De plus, une analyse des mécanismes d'endommagement est effectuée au moyen de la technique d'émission acoustique. Le comportement des poutres sandwiches sollicitées en flexion est ensuite étudié. Une attention particulière est portée à la compréhension des modes de rupture et à l'influence des variations locales des propriétés mécaniques de l'âme. Par ailleurs, certaines propriétés dynamiques de cette structure sont explorées, notamment son comportement en fatigue et sa réponse à l'impact afin de discuter de sa durabilité. Enfin, une étude expérimentale du comportement vibratoire des poutres composites et sandwiches est réalisée. Le rôle des différents constituants dans l'amortissement global des vibrations est discuté au moyen d'une modélisation par élément finis. L'ensemble des propriétés déterminées sont comparées à celles des matériaux non bio-sourcés, afin de situer ses performancesBio-based composites appear to be very promising alternatives to traditional composites. The use of natural fibres as reinforcement reduces the environmental impact of these materials and their specific properties are significantly increased. In this context, this work focuses on the manufacturing and the mechanical characterization of a bio-based sandwich structure. The skins are made of an innovative thermoplastic resin associated with flax fibres. The core is made of balsa wood. First, quasi-static analyses are performed on the different components. Then, the tensile properties of the composite skins are studied. Moreover, the main damage mechanisms are identified and described by means of the acoustic emission technique. Next, the flexural behavior of the whole sandwich structure is studied. Particular attention is paid to the detection and prediction of the main fracture modes. Moreover, the statistical spreads of the material properties of the balsa core are taken into account. In addition, cyclic fatigue and impact tests are performed to investigate the behavior of this structure under dynamic loads, and to discuss whether or not this material could be suitable for potential semi-structural applications. Finally, experimental analyses of the vibration behavior of composite and sandwich beams are performed. The contributions of the different components to the global damping properties of the sandwich structure are analyzed by means of a finite elements model. This work also compares the properties of this bio-based sandwich to those of traditional materials, in order to benchmark its mechanical performances with a view to further industrial usage
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Piñal, Moctezuma Juan Fernando. "Characterization of damage evolution on metallic components using ultrasonic non-destructive methods." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667641.
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When fatigue is considered, it is expected that structures and machinery eventually fail. Still, when this damage is unexpected, besides of the negative economic impact that it produces, life of people could be potentially at risk. Thus, nowadays it is imperative that the infrastructure managers, ought to program regular inspection and maintenance for their assets; in addition, designers and materials manufacturers, can access to appropriate diagnostic tools in order to build superior and more reliable materials. In this regard, and for a number of applications, non-destructive evaluation techniques have proven to be an efficient and helpful alternative to traditional destructive assays of materials. Particularly, for the design area of materials, in recent times researchers have exploited the Acoustic Emission (AE) phenomenon as an additional assessing tool with which characterize the mechanical properties of specimens. Nevertheless, several challenges arise when treat said phenomenon, since its intensity, duration and arrival behavior is essentially stochastic for traditional signal processing means, leading to inaccuracies for the outcome assessment.
In this dissertation, efforts are focused on assisting in the characterization of the mechanical properties of advanced high strength steels during under uniaxial tensile tests. Particularly of interest, is being able to detect the nucleation and growth of a crack throughout said test. Therefore, the resulting AE waves generated by the specimen during the test are assessed with the aim of characterize their evolution.
For this, on the introduction, a brief review about non-destructive methods emphasizing the AE phenomenon is introduced. Next is presented, an exhaustive analysis with regard to the challenge and deficiencies of detecting and segmenting each AE event over a continuous data-stream with the traditional threshold detection method, and additionally, with current state of the art methods. Following, a novel AE event detection method is proposed, with the aim of overcome the aforementioned limitations. Evidence showed that the proposed method (which is based on the short-time features of the waveform of the AE signal), excels the detection capabilities of current state of the art methods, when onset and endtime precision, as well as when quality of detection and computational speed are also considered. Finally, a methodology aimed to analyze the frequency spectrum evolution of the AE phenomenon during the tensile test, is proposed. Results indicate that it is feasible to correlate nucleation and growth of a crack with the frequency content evolution of AE events.Cuando se considera la fatiga de los materiales, se espera que eventualmente las estructuras y las maquinarias fallen. Sin embargo, cuando este daño es inesperado, además del impacto económico que este produce, la vida de las personas podría estar potencialmente en riesgo. Por lo que hoy en día, es imperativo que los administradores de las infraestructuras deban programar evaluaciones y mantenimientos de manera regular para sus activos. De igual manera, los diseñadores y fabricantes de materiales deberían de poseer herramientas de diagnóstico apropiadas con el propósito de obtener mejores y más confiables materiales. En este sentido, y para un amplio número de aplicaciones, las técnicas de evaluación no destructivas han demostrado ser una útil y eficiente alternativa a los ensayos destructivos tradicionales de materiales. De manera particular, en el área de diseño de materiales, recientemente los investigadores han aprovechado el fenómeno de Emisión Acústica (EA) como una herramienta complementaria de evaluación, con la cual poder caracterizar las propiedades mecánicas de los especímenes. No obstante, una multitud de desafíos emergen al tratar dicho fenómeno, ya que el comportamiento de su intensidad, duración y aparición es esencialmente estocástico desde el punto de vista del procesado de señales tradicional, conllevando a resultados imprecisos de las evaluaciones. Esta disertación se enfoca en colaborar en la caracterización de las propiedades mecánicas de Aceros Avanzados de Alta Resistencia (AAAR), para ensayos de tracción de tensión uniaxiales, con énfasis particular en la detección de fatiga, esto es la nucleación y generación de grietas en dichos componentes metálicos. Para ello, las ondas mecánicas de EA que estos especímenes generan durante los ensayos, son estudiadas con el objetivo de caracterizar su evolución. En la introducción de este documento, se presenta una breve revisión acerca de los métodos existentes no destructivos con énfasis particular al fenómeno de EA. A continuación, se muestra un análisis exhaustivo respecto a los desafíos para la detección de eventos de EA y las y deficiencias del método tradicional de detección; de manera adicional se evalúa el desempeño de los métodos actuales de detección de EA pertenecientes al estado del arte. Después, con el objetivo de superar las limitaciones presentadas por el método tradicional, se propone un nuevo método de detección de actividad de EA; la evidencia demuestra que el método propuesto (basado en el análisis en tiempo corto de la forma de onda), supera las capacidades de detección de los métodos pertenecientes al estado del arte, cuando se evalúa la precisión de la detección de la llegada y conclusión de las ondas de EA; además de, cuando también se consideran la calidad de detección de eventos y la velocidad de cálculo. Finalmente, se propone una metodología con el propósito de evaluar la evolución de la energía del espectro frecuencial del fenómeno de EA durante un ensayo de tracción; los resultados demuestran que es posible correlacionar el contenido de dicha evolución frecuencial con respecto a la nucleación y crecimiento de grietas en AAAR's.
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Martins, Alan. "Analysis of damage mechanisms in composite structures reinforced by tufting." Thesis, Compiègne, 2018. http://www.theses.fr/2018COMP2443/document.
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Cette étude portait sur l’évaluation des performances mécaniques et des mécanismes de défaillance des composites cousus dans différentes conditions de chargement. Des plaques stratifiées et des raidisseurs renforcés par tufting ont été fabriqués avec différents paramètres de couture afin d'évaluer leur effet sur les propriétés des composites. L'investigation a été assistée par une caractérisation multi-instrumentée pendant les tests. Les plaques cousues soumises à des tests de cisaillement à poutre courte sont utilisées dans l'analyse du comportement de la densité et de l'angle de couture dans des conditions de chargement en mode II, tandis que des tests d'impact et de compression après impact (CAI) sur la tolérance aux dommages. Des tests de fatigue en éprouvettes trouées ont également été réalisés afin d’évaluer la réponse des coutures, en particulier leur position par rapport au trou central, à la concentration de déformation générée par le trou. La suite de ce travail a consisté en des tests mécaniques sur panneau raidi oméga renforcé par tufting. La procédure a optimisé les paramètres de touffetage utilisés pour renforcer les structures du lot précédent d'échantillons jusqu'à atteindre un point optimal où les propriétés principales, principalement trouvées dans les tests d'arrachement, sont égales ou supérieures à celles des échantillons témoins. Cette amélioration tenait également compte des modifications de la forme des raidisseurs. En outre, une nouvelle approche basée sur l’effet piézorésistif des coutures en fibres de carbone lors du chargement des éprouvettes composites est réalisée. Cela peut faciliter la surveillance de l’état de santé des fils cousus et donc du composite en raison de la nature structurelle des coutures. Les résultats ont montré que les renforts par tufting sont capables d'augmenter considérablement la ténacité entre les composites et la tolérance aux endommagements des composites, principalement en raison de leurs phénomènes de pontage des fissures. Les paramètres de tufting sont des facteurs décisifs pour obtenir les meilleures propriétés mécaniques. Cependant, ces travaux ont montré que les fils de coutures sont également responsables de la création de fissures dues à la concentration de contrainte et aux défauts causés par leur insertion et, par conséquent, à la diminution de la résistance des composites. L'enquête conclut que l'insertion aléatoire des touffes n'est pas idéale pour la performance du matériau et doit donc être évitée. Le développement de l'insertion des coutures dans les raidisseurs oméga a été soutenu par la caractérisation multi-instrumentée qui a permis d'optimiser le renforcement de la structure. Bien que l’étude ait permis d’obtenir des propriétés mécaniques nettement supérieures à celles des panneaux oméga renforcés par touffetage, il est évident que la procédure employée n’est pas optimale. Le présent travail propose également un modèle préliminaire d'éléments finis pour surmonter le coût et la perte de temps des tests expérimentaux. Il vise principalement à optimiser les paramètres de tufting dans la structure. Le modèle développé était capable de prédire les mêmes endommagements que ceux observés expérimentalement, mais encore éloignés des prévisions quantitatives des résultats. Le contrôle de l’état structurel des stratifiés composites cousus par les fils de carbone semble prometteur et pourrait aider à l’avenir à fournir des informations sur l’état de santé des coutures sous chargement qui ne sont pas atteintes par les méthodes de caractérisation classiques utilisées dans ce travailThis study focused mainly on the assessment of the mechanical performance and the failure mechanisms of tufted composites under divers loading conditions. Laminated plates and stiffened panels reinforced by tufting was manufactured with different tufting parameters to evaluate their effect in the properties of the composites. Multi-instrumented characterization carried out during the tests assisted the investigation. The tufted plates subjected to short-beam shear tests aided especially in the behavior analysis of tufting density and angle in mode Il loading condition, while impact and compression after impact (CAI) tests on the damage tolerance. Open-hole fatigue tests were also performed to evaluate the tufts response, especially regarding their position to the center hole, to the strain concentration factor generated by the hole. The following part of this work consisted of the mechanical tests on omega stiffened panel reinforced by tufting. The procedure optimized the tufting parameters employed for reinforcing the structures from the previous batch of specimens until reaching an optimal point that the main properties, primarily found in pull-off tests, are equal or superior to those of the control specimens. This improvement also considered the modifications in the shape of the stiffeners. Furthermore, a novel approach based on the piezoresistive effect of carbon tufts under loading of the composite specimens is performed. This may support the monitoring of the health status on the tufted threads and therefore of the composite because of the structural nature of the tufts. The results showed that tufting reinforcements are capable of increasing the interlaminar fracture toughness and damage tolerance of the composites considerably owing mainly to their crack bridging phenomena. The tufting parameters are decisive factors for achieving the best mechanical properties. However, this work reported that tuft threads are also responsible for generating cracks due to the strain concentration and defects caused by their insertion and consequently, can decrease the strength of the composites. The investigation concludes that the random insertion of the tufts is not ideal for the performance of the material and thus must be avoided. The development of the tufting insertion in the omega stiffeners was supported by the multi-instrumented characterization that led to optimizing reinforcement in the structure. Although the study achieved the goal of obtaining mechanical properties significantly superior to the omega panels reinforced by tufting, it is noticeable that the procedure employed is not optimal. The present work also proposes a preliminary finite element model to overcome the costly and time consuming of the experimental tests. It intends primarily optimizing the tufting parameters in the structure. The model developed was capable of predicting the same damage events as observed experimentally, but it still distant from the quantitative predictions of the results. The structural health monitoring of the tufted composite laminates by the carbon threads seems promising and could help in the future for supplying data about the tufts health status under loading that are not achieved by the conventional characterization methods employed in this work
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Barbière, Romain. "Comportement en fatigue et optimisation de l’interface d’un composite tissé chanvre/époxy : effet de l’humidité Influence of moisture and drying on fatigue damage mechanisms in a woven hemp/epoxy composite : acoustic emission and micro-CT analysis." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2020. http://www.theses.fr/2020ESMA0016.
Full textAbstract:
Les composites à renfort d’origine végétale constituent une alternative écologique aux matériaux composites traditionnels tels que les composites à fibres de verre. Cependant, les renforts d’origine végétale sont fortement hydrophiles par rapport à la matrice polymère. Il est donc nécessaire d’étudier l’influence de l’eau sur le comportement mécanique de ces éco-matériaux.Dans ce travail, trois conditionnements ont été mis en place. Le conditionnement Ambiant correspond à l’étude du composite en environnement ambiant : stockage et essais à l’ambiante. Le conditionnement Eau permet d’étudier les échantillons dans des conditions extrêmes d’humidité : les éprouvettes sont saturées en eau puis testées dans une enceinte saturée en humidité. Le conditionnement Séché a pour objectif d’étudier le rôle de la désorption sur les propriétés mécaniques du composite. Des éprouvettes de composite tissé chanvre/époxy de deux orientations, [(0/90)]7 et [(±45)]7, ont été testées en traction et en fatigue suivant les trois conditionnements. Des analyses in situ par émission acoustique et post-mortem par MEB et microtomographie ont été réalisées.Les essais de fatigue ont permis d’établir les courbes de Wöhler pour les deux orientations et les trois conditionnements. Un modèle phénoménologique a été utilisé pour modéliser la durée de vie du composite dans toutes les configurations. Les comparaisons montrent que le conditionnement Eau a une sensibilité à la fatigue plus faible que les conditionnements Ambiant et Séché. La classification des évènements acoustiques a permis d’identifier trois classes correspondant chacune à un type d’endommagement (endommagement matriciel, endommagement interfacial et rupture de fibres). Pour les deux orientations, les résultats ont montré que la proportion en nombre et la cinétique d’apparition de chaque type d’endommagement dépendent du niveau de contrainte maximale appliquée et du type de conditionnement, les endommagements matriciels et interfaciaux étant toujours largement majoritaires. L’analyse microtomographique a montré que les endommagements sont différents selon l’orientation. Cependant, pour chaque orientation, on retrouve le même type d’endommagement pour les trois conditionnements, à différents stades de développement : plus avancé pour le conditionnement Eau, intermédiaire pour le Séché et le moins développé pour l’Ambiant.Pour analyser l’adhésion à l’interface fil/matrice, des tests de fragmentation ont été réalisés sur des éprouvettes monofilamentaires chanvre/époxy. Un moule spécifique a été conçu et développé pour réaliser ces éprouvettes par coulée. Un suivi par émission acoustique couplé à des observations en lumière polarisée a permis de mieux comprendre le phénomène de fragmentation dans ce type d’éprouvettes. Les valeurs de la contrainte maximale de cisaillement à l’interface fil/matrice (IFSS) ont été calculées et les longueurs de décohésion interfaciale ont été mesurées. Les résultats montrent que l’interface fil/matrice est affaiblie après séchage, avec une diminution de l’IFSS de 33%. Pour améliorer l’adhésion à l’interface, un traitement au peroxyde d’hydrogène et un traitement par plasma froid ont été appliqués au renfort de chanvre. Les tests de fragmentation montrent que l’IFSS est presque deux fois plus élevée avec le traitement au peroxyde et trois fois plus avec le plasma, par rapport aux éprouvettes non traitées. Un changement d’échelle a ensuite été effectué en appliquant le traitement au peroxyde d’hydrogène sur le tissu de chanvre. Le comportement en traction et en fatigue des composites chanvre/époxy élaborés avec ce tissu traité a été étudié. Les résultats obtenus à cette échelle ne sont pas satisfaisants. Le traitement par plasma reste donc la voie la plus prometteuse, mais appliquer cette technique à l’échelle d’un tissu est complexe et nécessite de mettre au point un nouveau réacteurPlant fibre composites are an environmentally friendly alternative to traditional composite materials such as fibreglass composites. However, plant fibres are highly hydrophilic in comparison with the polymer matrix. It is therefore necessary to study the influence of moisture on the mechanical behaviour of these eco-materials.In this work, three conditionings were applied. “Ambient” samples were stored and tested in ambient environment. “Wet” samples were immersed in water until saturation and tested in a climatic chamber at RH97. The objective of the “Wet/Dry” conditioning was to study the role of desorption on the mechanical properties of the composite. Woven hemp/epoxy composite samples with two orientations, [(0/90)]7 and [(± 45)]7, were tested in tension and fatigue according to the three conditionings. In situ analyses by acoustic emission and post-mortem analyses by SEM and micro-CT were carried out.Fatigue tests allowed to determine the Wöhler curves for the two orientations and the three conditionings. A phenomenological model was used to simulate the fatigue life of the composite in all configurations. The comparisons showed that the Wet samples exhibit a lower tensile strength than the Ambient specimens and a lower fatigue sensitivity, while the behaviour of the Wet/dry samples is similar to the Wet conditioning one concerning the tensile strength and similar to the Ambient one concerning the fatigue sensitivity. The classification of acoustic events allowed the identification of three clusters, each cluster corresponding to a type of damage (matrix damage, interfacial damage and fibre breakage). For the two orientations, the results showed that the proportion in number and the kinetics of development of each type of damage depend on the level of the maximum applied stress and on the conditioning. Matrix and interfacial damages are largely the most numerous acoustic events for all the configurations. Micro-CT analysis showed that the damage is different depending on the orientation. However, for each orientation, the same type of damage is observed for the three conditionings, at different stages of development: more advanced for the Wet conditioning, intermediate for the Wet/Dry one and the least developed for the Ambient one.The analysis of the yarn/matrix interface adhesion was performed through fragmentation tests realised on monofilament hemp/epoxy specimens. A specific mould was designed and developed to produce these specimens by casting. Acoustic emission monitoring and observations in polarized light allowed a better understanding of the fragmentation phenomenon in this type of material. The Interfacial Shear Strength (IFSS) values were calculated and the interfacial debonding lengths were measured. The results show that the yarn/matrix interface is weakened after drying, with a decrease in IFSS of 33%. To improve adhesion at the interface, treatments with hydrogen peroxide and non-thermal plasma were applied to the hemp yarns. Fragmentation tests showed that IFSS is almost twice as high with the peroxide treatment and three times higher with plasma, compared to untreated specimens. An upscale was made by applying the hydrogen peroxide treatment to the hemp fabric. The tensile and fatigue behaviour of hemp/epoxy composites produced with this treated fabric was studied. The results obtained at this scale are disappointing. Therefore, the non-thermal plasma treatment remains the most promising solution, but applying this technique at the fabric scale is complex and requires the development of a new reactor
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Kang, Bong-Gu, Joachim Hannawald, and Wolfgang Brameshuber. "Schallemissionsanalyse zur Untersuchung des Schädigungsverhaltens im Auszugversuch eines in Beton eingebetteten Multifilamentgarns." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1244045098499-20524.
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Zur Untersuchung der Schädigungs- und Versagensmechanismen eines in Beton eingebetteten Multifilamentgarns im Auszugversuch wurde die Schallemissionsanalyse zur Identifizierung und Lokalisierung von Filamentbrüchen eingesetzt. Im ersten Schritt wurden dazu die Schall emittierenden Ursachen (Filamentriss, Filamentablösung und Mikroriss im Beton) für eine Differenzierung charakterisiert. Es wurden Versuche zur Erzeugung von isolierten Signalen durchgeführt, welche mit Hilfe der Signal- und Frequenzanalyse untersucht wurden. Bei dem durchgeführten Garnauszugversuch konnte eine hohe Lokalisierungsgenauigkeit der Filamentbrüche erzielt werden. Der Schädigungsverlauf des Garns während des Auszugversuchs konnte detailliert untersucht werden.
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Traore, Oumar Issiaka. "Méthodologie de traitement et d'analyse de signaux expérimentaux d'émission acoustique : application au comportement d'un élément combustible en situation accidentelle." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0011/document.
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L’objectif de cette thèse est de contribuer à l’amélioration du processus de dépouillement d’essais de sûreté visant étudier le comportement d'un combustible nucléaire en contexte d’accident d’injection de réactivité (RIA), via la technique de contrôle par émission acoustique. Il s’agit notamment d’identifier clairement les mécanismes physiques pouvant intervenir au cours des essais à travers leur signature acoustique. Dans un premier temps, au travers de calculs analytiques et des simulation numériques conduites au moyen d’une méthode d’éléments finis spectraux, l’impact du dispositif d’essais sur la propagation des ondes est étudié. Une fréquence de résonance du dispositif est identifiée. On établit également que les mécanismes basses fréquences ne sont pas impactés par le dispositif d'essais. En second lieu, diverses techniques de traitement du signal (soustraction spectrale, analyse spectrale singulière, ondelettes. . . ) sont expérimentées, afin de proposer des outils permettant de traiter différent types de bruit survenant lors des essais RIA. La soustraction spectrale s’avère être la méthode la plus robuste aux changements de nature du bruit, avec un fort potentiel d’amélioration du rapport signal-à-bruit. Enfin, des méthodes d’analyse de données multivariées et d’analyse de données fonctionnelles ont été appliquées, afin de proposer un algorithme de classification statistique permettant de mieux comprendre la phénoménologie des accidents de type RIA et d’identifier les mécanismes physiques. Selon l’approche (multivariée ou fonctionnelle), les algorithmes obtenus permettent de reconnaître le mécanisme associé à une salve dans plus de 80% des casThe objective of the thesis is to contribute to the improvement of the monitoring process of nuclear safety experiments dedicated to study the behavior of the nuclear fuel in a reactivity initiated accident (RIA) context, by using the acoustic emission technique. In particular, we want to identify the physical mechanisms occurring during the experiments through their acoustic signatures. Firstly, analytical derivations and numerical simulations using the spectral finite element method have been performed in order to evaluate the impact of the wave travelpath in the test device on the recorded signals. A resonant frequency has been identified and it has been shown that the geometry and the configuration of the test device may not influence the wave propagation in the low frequency range. Secondly, signal processing methods (spectral subtraction, singular spectrum analysis, wavelets,…) have been explored in order to propose different denoising strategies according to the type of noise observed during the experiments. If we consider only the global SNR improvement ratio, the spectral subtraction method is the most robust to changes in the stochastic behavior of noise. Finally, classical multivariate and functional data analysis tools are used in order to create a machine learning algorithm dedicated to contribute to a better understanding of the phenomenology of RIA accidents. According to the method (multivariate or functional), the obtained algorithms allow to identify the mechanisms in more than 80 % of cases
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Saavedra, Patricia Carolina Alejandra Rodríguez. "Análise do microfissuramento em rochas no ensaio de compressão diametral por meio da técnica de emissão acústica." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/18/18132/tde-10072017-095950/.
Full textAbstract:
Em nível microscópico, as rochas apresentam microdefeitos que agem como concentradores locais de tensão, favorecendo a ocorrência de ruptura frágil. O entendimento desse processo requer análises experimentais em rochas submetidas a tensões de tração. O ensaio de compressão diametral é uma alternativa apropriada, pois não apresenta as dificuldades envolvidas no ensaio de tração direta. A propagação de microfissuramento em materiais frágeis produz liberação de energia na forma de ondas elásticas chamadas de emissões acústicas (EA). O monitoramento com EA permite acompanhar a propagação de dano no corpo de prova (CP), sem perturbá-lo. Nesta pesquisa, CPs de mármore e monzogranito são submetidos a ensaios de compressão diametral com deslocamentos monotônicos e cíclicos, com controle de deslocamento. Aplica-se a técnica de EA, em conjunto com análises petrográficas, análises das curvas de força versus deslocamento e exame visual, para caracterizar o seu processo de microfissuramento. A localização tridimensional das fontes de EA foi realizada inicialmente utilizando-se o software AEwin® da PASA. Foi desenvolvido um programa de localização aprimorado que incorpora o cálculo da velocidade de propagação das ondas (vp) média para cada instante em que uma fonte é localizada. O novo programa (Crack Location by Acoustic emission with P Wave Velocity determination, CLAPWaVe) mostra um claro decréscimo da velocidade de propagação com o aumento do dano. O programa desenvolvido (CLAPWaVe) mostrou melhor ajuste e maior coerência com a literatura e com a condição final rompida dos CPs do que o software AEwin. Em mármore e monzogranito o microfissuramento se inicia a 25-30% e 75-85% do carregamento de pico, respectivamente, e localiza-se na vizinhança do centro do CP. Em ambas as rochas se acumulou, também, dano na região dos apoios do CP, associado à transferência de carregamento do berço ao CP. Antes do pico de carregamento, o microfissuramento tornou-se mais denso e localizado no centro e nos apoios do CP, embora a região central ainda concentre a maior parte. Após o pico, o microfissuramento acumulou-se em uma das faces do CP, progredindo até a outra face. O monzogranito apresentou ruptura progressiva do CP, enquanto que no mármore a maior parte da superfície de ruptura já está desenvolvida imediatamente após o pico. Durante o ensaio em ambas as rochas, no núcleo central foram registradas as menores velocidades vp do CP. Na região dos apoios, embora tenha havido microfissuramento, registraram-se as maiores velocidades vp no CP, pois o confinamento produzido pelo contato com o berço aumentou localmente a rigidez do CP. A distribuição não homogênea de vp no CP revelou que a consideração desse parâmetro como constante e igual à condição intacta ao longo do ensaio, como comumente encontrado na literatura, não representa a condição real do CP danificado. O microfissuramento no monzogranito se propaga principalmente através dos cristais de quartzo, seguindo um caminho tortuoso subparalelo à direção de carregamento e liberando altos níveis de energia absoluta. No mármore, a propagação segue os planos de clivagem da calcita, liberando níveis baixos de energia absoluta. Os histogramas da distribuição espacial da resistência em ambas as rochas mostraram bom ajuste a uma distribuição de Weibull, porém o monzogranito mostrou melhor ajuste e menor variabilidade que o mármore. As análises dos sinais no domínio das frequências mostraram que o microfissuramento é caracterizado por emissões de banda larga.At microscopic level, rocks exhibit microflaws, which act as local stress concentrators, favoring the occurrence of brittle failure. The understanding of this process requires experimental analyses of rock specimens under tensile stresses. The diametral compression test is an adequate alternative for such a studies, because it does not present the difficulties of direct tension tests. Crack propagation in brittle materials releases energy as transient elastic waves known as acoustic emission (AE). Monitoring with AE enables an insight into the cracking process without affecting the integrity of the sample. In this work, marble and monzogranite specimens were subjected to monotonic and cyclic displacementcontrolled diametral compression tests. The AE monitoring technique was applied in conjunction with petrographic analyses, interpretation of the load versus displacement curves and visual examination of the samples for the characterization of their cracking process. The three-dimensional localization of the AE sources was initially carried out by using the software AEwin® from PASA. An improved localization software, which considers the P-wave velocity variation along the damage process (vp) for each AE source was developed. The developed software (Crack Location by Acoustic emission with P Wave Velocity determination, CLAPWaVe) has shown greater consistency with literature and the final cracked samples and better accuracy than AEwin. Microcracking in monzogranite and marble initiated at 25-30% and 75-80% of the peak load, respectively, and is located at the center of the specimen. In addition, both rocks showed concentrated microcracking close to the region of contact between the specimen and the loading platens, related to the loading transference along the loading edge. Before peak load, microcracking becomes denser and localized at the center and the contact region of the specimen, although, the central region still concentrates the main portion of the damage. After the peak load, new microcracks were first concentrated on one of the faces at the center of the specimen and then propagated through its thickness all the way to the other face. The progressive failure in monzogranite extended through to the end of the test, while in marble the main portion of the failure surface of the specimen developed just after peak. During the whole test in both rocks, the lowest velocities (vp) of the specimen were recorded in the central core. Although microcracking was induced at the contact region, the highest velocities vp of the specimen were registered there, because of the confinement effect produced by the platens, which lead to a local increase in the stiffness of the specimen. The non-homogeneous distribution of vp in the specimen has revealed that the utilization of this parameter as a constant and equal to the value measured in the specimen before testing (as usually adopted in the literature), does not represent the real condition of the damaged specimen. In monzogranite, microcracks propagate mainly through quartz crystals, following a tortuous path subparallel to the loading direction, by releasing high-level of absolute energy, while in marble the propagation of microcracks follows the cleavage planes of calcite, by releasing low-level of absolute energy. The histograms of spatial strength distribution in both rocks have shown good adjustment to a Weibull distribution, but monzogranite exhibited a more accurate adjustment with lower variability than marble. The analysis of signals in the frequency domain showed that the microcracking is characterized by wide band emissions.
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De, Oliveira Rui Fernando Berthelot Jean-Marie Torres Marques Antonio. "Health monitoring of FRP using acoustic emission and fibre optic techniques." [S.l.] : [s.n.], 2005. http://cyberdoc.univ-lemans.fr/theses/2005/2005LEMA1027.pdf.
Full textAbstract:
Reproduction de : Thèse de doctorat : Génie mécanique et productique : Le Mans : 2005. Reproduction de : Thèse de doctorat : Génie mécanique et productique : Porto : 2005.Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Bibliogr. p. 206-237.
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De, Oliveira Rui Fernando. "Health monitoring of FRP using acoustic emission and fibre optic techniques." Le Mans, 2005. http://cyberdoc.univ-lemans.fr/theses/2005/2005LEMA1027.pdf.
Full textAbstract:
Dans cette dissertation est proposée une procédure pour le suivi en continu de l'endommagement dans les PRF à partir de l'émission acoustique (EA). Deux matériaux ont été étudiés afin d'associer les ondes d'EA aux mécanismes d'endommagement source : l'éprouvette monofilamentaire et le stratifié croisé. Ces matériaux ont été choisis pour avoir une séquence d'endommagement bien établie. Pour ces matériaux, le processus de fracture a pu être contrôlé, avec une raisonnable efficacité, en changeant certaines conditions d'essais. Une fois les conditions d'endommagement changées il a été possible d'établir des relations avec les ondes d'EA détectées. Un traitement hybride du signal d'EA a été implémenté basé sur l'analyse de la forme d'onde et le contenu fréquentiel. Les réseaux de neurones à apprentissage non supervisé ont été appliqués à la classification automatique des signaux transitoires d'EA détectés au cour de l'essai des stratifiés croisés. Une représentation temps-fréquence des signaux classifiés a été implémentée en utilisant la transformée en ondelette afin de rehausser les caractéristiques des signaux. Les mécanismes d'endommagement ont pu être identifiés à partir de l'analyse modale des signaux d'EA. Un système de capteur à fibre optique basé sur un interféromètre de Fabry-Pérot à fibre optique a été conçu afin de détecter les ondes d'EA. Deux procédures originales d'interrogation de la cavité basées sur la génération de deux signaux en quadrature de phase ont été proposées afin de récupérer la phase. La capacité du système de capteur à fibre optique à détecter les ondes d'EA simulées a été montréeIn this dissertation is proposed a procedure for continuous damage monitoring of FRP (fibre reinforced plastics), from the rapid release of elastic strain energy, generated at damage, in the form of elastic waves (acoustic emission). Two materials were studied in order to associate the acoustic emission waves to the damage mechanisms source : the single fibre specimen and cross-ply laminate. Those materials were chosen for having well established damage sequence. For these materials, the fracture process could be controlled, with reasonable efficiency, changing some tests conditions. Once the damage conditions changed it was possible to establish relationships with the detected acoustic emission waves. A hybrid processing of acoustic emission signals was implemented based on waveform and frequency analysis. Unsupervised artificial neural networks were used for automated clustering of transient acoustic emission signals detected during testing of the cross-ply laminates. A time-frequency representation of the classified signals was implemented using the wavelet transform for signal characteristics enhancement. Damage mechanisms could be identified from the modal analysis of the acoustic emission waves. An optical fibre sensor system was conceived for acoustic emission waves detection based on an optical fibre Fabry-Pérot interferometer. Two original interrogation procedures based upon the generation of two quadrature-shifted signals for phase recovery were proposed. The capability of the optical fibre sensor system to detect simulated acoustic emission waves was shown
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Bobich, Jennifer Kay. "Experimental analysis of the extension to shear fracture transition in Berea Sandstone." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2584.
Full textAbstract:
To characterize low-pressure, brittle deformation in porous, granular rock, notchcut
cylinders (30 mm neck diameter) of Berea Sandstone were extended in a triaxial
apparatus from 10 to 160 MPa confining pressure at strain rates of 10-4 s-1 and 10-5 s-1.
Acoustic emission counts were monitored when extending samples at a slow strain rate.
Stress at fracture is characterized by the least compressive principal stress, ??3, and
maximum compressive principal stress, ??1 (??1 = Pc). A change in strength dependence
on pressure at Pc = 50 MPa corresponds to a change from pure macroscopic extension
fracture to mixed-mode opening and shear fracture, and likely reflects the increase in
mean stress that suppresses the propagation of extension fractures and the interaction
between closely-spaced stepped cracks. Within the extension fracture regime (Pc < 50
MPa), ??3 at failure becomes slightly more tensile with an increase in Pc. At Pc > 50
MPa, ??3 at failure becomes more compressive with an increase in Pc and follows
Coulomb behavior; however, the angle between the fracture surface and ??1 increases
continuously with Pc. Fracture surfaces characteristic of the extension to shear fracture
transition appear as linked, stepped extension fractures; the length of extensional
segments decreases with increasing pressure. The onset of acoustic emissions and inelastic strain at fracture occurs at earlier points in the strain history with pressure,
consistent with the Griffith prediction of the beginning of fracture growth.