Barium osumilite (BMAS) ceramic matrix composites reinforced with SiC-Tyranno fibers are tested i... more Barium osumilite (BMAS) ceramic matrix composites reinforced with SiC-Tyranno fibers are tested in a cyclic loading protocol. Broadband acoustic emission (AE) sensors are used for monitoring the occurrence of different possible damage mechanisms. Improved use of AE indices is proposed by excluding low-severity signals based on waveform parameters, rather than only threshold criteria. The application of such improvements enhances the accuracy of the indices as accumulated damage descriptors. RA-value, duration, and signal energy follow the extension cycles indicating moments of maximum or minimum strain, while the frequency content of the AE signals proves very sensitive to the pull-out mechanism.
ABSTRACT Conference code: 105020, Export Date: 5 June 2014, CODEN: PSISD, Correspondence Address:... more ABSTRACT Conference code: 105020, Export Date: 5 June 2014, CODEN: PSISD, Correspondence Address: Matikas, T.E.; Department of Materials Science and Engineering, University of Ioannina, Ioannina, 45110, Greece, References: Maldague, X.P.V., Introduction to NDT by active infrared thermography (2002) Materials Evaluation, 60 (9), pp. 1060-1073;
ABSTRACT Infrared thermography is a powerful non-destructive testing technique which can be used ... more ABSTRACT Infrared thermography is a powerful non-destructive testing technique which can be used for the detection of damage in advanced materials such as ceramic matrix composites. The purpose of this study is to apply a non-destructive methodology for analyzing, in real-time, the thermal effects in ceramic matrix composites caused by cyclic loading. Mechanical stresses induced by cyclic loading cause heat release in the composite due to failure of the interface, which results in increasing the material’s temperature. The heat waves, generated by the thermo-mechanical coupling, and the intrinsic energy dissipated during mechanical cyclic loading of the specimen, were detected by an infrared camera. The results were correlated with acoustic emission events that occurred during the damage accumulation process of the material.
Smart Sensor Phenomena, Technology, Networks, and Systems Integration 2012, 2012
ABSTRACT Infrared thermography is one of several non-destructive testing techniques which can be ... more ABSTRACT Infrared thermography is one of several non-destructive testing techniques which can be used for detection of damage in materials such as ceramic matrix composites. The purpose of this study is to apply a non-destructive methodology for analyzing the thermal effects in ceramic matrix composites caused by cyclic loading. Mechanical stresses induced by cyclic loading cause heat release in the composite due to failure of the interface, which results in increasing the material's temperature. The heat wave, generated by the thermo-mechanical coupling, and the intrinsic energy dissipated during mechanical cyclic loading of the sample were detected by an infrared camera. The results were correlated with acoustic emission events.
One of the most frequent problems in concrete structures is corrosion of metal reinforcement. It ... more One of the most frequent problems in concrete structures is corrosion of metal reinforcement. It occurs when the steel reinforcement is exposed to environmental agents. The corrosion products occupy greater volume than the steel consumed, leading to internal expansion stresses. When the stresses exceed concrete strength, eventually lead to corrosion-induced cracking beneath the surface. These cracks do not show any
A combination of nondestructive testing techniques is applied in this paper for the detection and... more A combination of nondestructive testing techniques is applied in this paper for the detection and characterization of subsurface damage in concrete. Thermography is initially used to locate the defects, in the form of vertical cracks beneath the surface, due to the variation of the temperature field as monitored by an infrared camera. Additionally, cooling down curves enhance the characterization by
Emerging Technologies in Non-Destructive Testing V, 2012
ABSTRACT Infrared thermography is a real-time method based on monitoring the temperature variatio... more ABSTRACT Infrared thermography is a real-time method based on monitoring the temperature variation on the surface of materials and structures. This method identifies and interprets the surface temperature differences in the material, leading to the evaluation of damage distribution and accumulation. Infrared thermography is a non-destructive, full field and non-contact method allowing characterization of degradation in historic monuments without causing further damage to them. This work presents recent results of infrared thermographic inspection of murals at the "Monastery of Molivdoskepastos" in the Ioannina region (Greece). Three different thermographic methods have been used and compared for their efficiency in detecting hidden letters in sub-surface donor's inscriptions.
Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2014, 2014
ABSTRACT In this work an innovative methodology was employed for monitoring the fracture behavior... more ABSTRACT In this work an innovative methodology was employed for monitoring the fracture behavior in silicon carbide fiberreinforced ceramic matrix composites. This new methodology was based on the combined use of IR thermography and acoustic emission. Compact tension SiC/BMAS specimens were tested with unloading/reloading loops and the thermal dissipation due to crack propagation and other damage mechanisms was monitored by IR thermography. The accuracy of this technique was benchmarked by optical measurements of crack length. In addition, using acoustic emission descriptors, such as activity during the unloading part of the cycles, provided the critical level of damage accumulation in the material. Acoustic emission allowed to closely follow the actual crack growth monitored by IR thermography, enabling quantitative measurements.
Smart Sensor Phenomena, Technology, Networks, and Systems 2011, 2011
Acoustic Emission (AE) supplies information on the fracturing behavior of different materials. In... more Acoustic Emission (AE) supplies information on the fracturing behavior of different materials. In this study, AE activity was recorded during fatigue experiments in metal CT specimens with a V-shape notch which were loaded in fatigue until final failure. AE parameters exhibit a sharp increase approximately 1000 cycles before than final failure. Therefore, the use of acoustic emission parameters is discussed both in terms of characterization of the damage mechanisms, as well as a tool for the prediction of ultimate life of the material under fatigue. Additionally, an innovative nondestructive methodology based on lock-in thermography is developed to determine the crack growth rate using thermographic mapping of the material undergoing fatigue. The thermographic results on the crack growth rate of aluminium alloys were then correlated with measurements obtained by the conventional compliance method, and found to be in agreement.
Smart Sensor Phenomena, Technology, Networks, and Systems 2011, 2011
ABSTRACT The purpose of this study is to develop an innovative non-destructive methodology for an... more ABSTRACT The purpose of this study is to develop an innovative non-destructive methodology for analyzing the thermal effects in metallic materials caused by fatigue. Mechanical stresses induced by cyclic loading in the material cause heat release due to microstructural changes, which results in an increase of the material's temperature. The heat release was quantified as a function of fatigue cycles in carbon steel samples. Mechanical hysteresis phenomena were analyzed to identify the metrics of damage, which relates to thermal parameters characterizing the level of damage of the material as a function of fatigue cycles.
Smart Sensor Phenomena, Technology, Networks, and Systems Integration 2012, 2012
ABSTRACT Composite materials are widely used especially in the aerospace structures and systems. ... more ABSTRACT Composite materials are widely used especially in the aerospace structures and systems. Therefore, inexpensive and efficient damage identification is crucial for the safe use and function of these structures. In these structures low-velocity impact is frequently the cause of damage, as it may even be induced during scheduled repair. Flaws caused by lowvelocity impact are dangerous as they may further develop to extended delaminations. For that purpose an effective inspection of defects and delaminations is necessary during the service life of the aerospace structures. Within the scope of this work, an innovative technique is developed based on current stimulating thermography. Electric current is injected to Carbon Fiber Reinforced Composite and aluminium (Al) plates with concurrent thermographic monitoring. For reference, both damaged and undamaged plates are inspected. Low-velocity impact damaged composite laminates at different energy levels are interrogated employing the novel technique. Live and pulse phase infrared thermography is employed for the identification of low-velocity impact damage at various energy levels while the electric current induces the transient thermal field in the vicinity of the defect. In all cases conventional ultrasonics (C-scan) were performed for the validation and assessment of the results of the innovative thermographic method.
ABSTRACT Acoustic emission (AE) supplies information on the fracturing behavior of different mate... more ABSTRACT Acoustic emission (AE) supplies information on the fracturing behavior of different materials. In this study, AE activity was recorded during fatigue experiments in metal coupons. The plates were characterized by a symmetric V-shape notch and were loaded in tension–tension fatigue until final failure with concurrent AE activity monitoring. The relatively broad bandwidth of the sensors enabled the recording of a wide range of frequencies up to 1MHz. AE parameters like energy and duration exhibited a certain increase with the accumulation of damage although the hit rate was not significantly influenced. Furthermore the behavior of RA value (ratio of rise time to amplitude of the waveforms) which quantifies the shape of the first part of the AE signals and has been used for characterization of the cracking mode, showed a certain shift indicating the transition from tensile mode to shear which can be confirmed by the visual observation of the crack geometry after the experiment. The time history of RA is similar to the crack propagation rate (da/dN) curve but exhibits the rapid hyperbolic growth consistently about 1000 cycles earlier than final failure. Therefore, the use of acoustic emission parameters is discussed both in terms of characterization of the damage mechanisms, as well as a tool for the prediction of ultimate life of the material under fatigue.
ABSTRACT Infrared thermography is a powerful non-destructive testing technique which can be used ... more ABSTRACT Infrared thermography is a powerful non-destructive testing technique which can be used for the detection of damage in advanced materials such as ceramic matrix composites. The purpose of this study is to apply a non-destructive methodology for analyzing, in real-time, the thermal effects in ceramic matrix composites caused by cyclic loading. Mechanical stresses induced by cyclic loading cause heat release in the composite due to failure of the interface, which results in increasing the material’s temperature. The heat waves, generated by the thermo-mechanical coupling, and the intrinsic energy dissipated during mechanical cyclic loading of the specimen, were detected by an infrared camera. The results were correlated with acoustic emission events that occurred during the damage accumulation process of the material.
Barium osumilite (BMAS) ceramic matrix composites reinforced with SiC-Tyranno fibers are tested i... more Barium osumilite (BMAS) ceramic matrix composites reinforced with SiC-Tyranno fibers are tested in a cyclic loading protocol. Broadband acoustic emission (AE) sensors are used for monitoring the occurrence of different possible damage mechanisms. Improved use of AE indices is proposed by excluding low-severity signals based on waveform parameters, rather than only threshold criteria. The application of such improvements enhances the accuracy of the indices as accumulated damage descriptors. RA-value, duration, and signal energy follow the extension cycles indicating moments of maximum or minimum strain, while the frequency content of the AE signals proves very sensitive to the pull-out mechanism.
Barium osumilite (BMAS) ceramic matrix composites reinforced with SiC-Tyranno fibers are tested i... more Barium osumilite (BMAS) ceramic matrix composites reinforced with SiC-Tyranno fibers are tested in a cyclic loading protocol. Broadband acoustic emission (AE) sensors are used for monitoring the occurrence of different possible damage mechanisms. Improved use of AE indices is proposed by excluding low-severity signals based on waveform parameters, rather than only threshold criteria. The application of such improvements enhances the accuracy of the indices as accumulated damage descriptors. RA-value, duration, and signal energy follow the extension cycles indicating moments of maximum or minimum strain, while the frequency content of the AE signals proves very sensitive to the pull-out mechanism.
ABSTRACT Conference code: 105020, Export Date: 5 June 2014, CODEN: PSISD, Correspondence Address:... more ABSTRACT Conference code: 105020, Export Date: 5 June 2014, CODEN: PSISD, Correspondence Address: Matikas, T.E.; Department of Materials Science and Engineering, University of Ioannina, Ioannina, 45110, Greece, References: Maldague, X.P.V., Introduction to NDT by active infrared thermography (2002) Materials Evaluation, 60 (9), pp. 1060-1073;
ABSTRACT Infrared thermography is a powerful non-destructive testing technique which can be used ... more ABSTRACT Infrared thermography is a powerful non-destructive testing technique which can be used for the detection of damage in advanced materials such as ceramic matrix composites. The purpose of this study is to apply a non-destructive methodology for analyzing, in real-time, the thermal effects in ceramic matrix composites caused by cyclic loading. Mechanical stresses induced by cyclic loading cause heat release in the composite due to failure of the interface, which results in increasing the material’s temperature. The heat waves, generated by the thermo-mechanical coupling, and the intrinsic energy dissipated during mechanical cyclic loading of the specimen, were detected by an infrared camera. The results were correlated with acoustic emission events that occurred during the damage accumulation process of the material.
Smart Sensor Phenomena, Technology, Networks, and Systems Integration 2012, 2012
ABSTRACT Infrared thermography is one of several non-destructive testing techniques which can be ... more ABSTRACT Infrared thermography is one of several non-destructive testing techniques which can be used for detection of damage in materials such as ceramic matrix composites. The purpose of this study is to apply a non-destructive methodology for analyzing the thermal effects in ceramic matrix composites caused by cyclic loading. Mechanical stresses induced by cyclic loading cause heat release in the composite due to failure of the interface, which results in increasing the material's temperature. The heat wave, generated by the thermo-mechanical coupling, and the intrinsic energy dissipated during mechanical cyclic loading of the sample were detected by an infrared camera. The results were correlated with acoustic emission events.
One of the most frequent problems in concrete structures is corrosion of metal reinforcement. It ... more One of the most frequent problems in concrete structures is corrosion of metal reinforcement. It occurs when the steel reinforcement is exposed to environmental agents. The corrosion products occupy greater volume than the steel consumed, leading to internal expansion stresses. When the stresses exceed concrete strength, eventually lead to corrosion-induced cracking beneath the surface. These cracks do not show any
A combination of nondestructive testing techniques is applied in this paper for the detection and... more A combination of nondestructive testing techniques is applied in this paper for the detection and characterization of subsurface damage in concrete. Thermography is initially used to locate the defects, in the form of vertical cracks beneath the surface, due to the variation of the temperature field as monitored by an infrared camera. Additionally, cooling down curves enhance the characterization by
Emerging Technologies in Non-Destructive Testing V, 2012
ABSTRACT Infrared thermography is a real-time method based on monitoring the temperature variatio... more ABSTRACT Infrared thermography is a real-time method based on monitoring the temperature variation on the surface of materials and structures. This method identifies and interprets the surface temperature differences in the material, leading to the evaluation of damage distribution and accumulation. Infrared thermography is a non-destructive, full field and non-contact method allowing characterization of degradation in historic monuments without causing further damage to them. This work presents recent results of infrared thermographic inspection of murals at the "Monastery of Molivdoskepastos" in the Ioannina region (Greece). Three different thermographic methods have been used and compared for their efficiency in detecting hidden letters in sub-surface donor's inscriptions.
Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2014, 2014
ABSTRACT In this work an innovative methodology was employed for monitoring the fracture behavior... more ABSTRACT In this work an innovative methodology was employed for monitoring the fracture behavior in silicon carbide fiberreinforced ceramic matrix composites. This new methodology was based on the combined use of IR thermography and acoustic emission. Compact tension SiC/BMAS specimens were tested with unloading/reloading loops and the thermal dissipation due to crack propagation and other damage mechanisms was monitored by IR thermography. The accuracy of this technique was benchmarked by optical measurements of crack length. In addition, using acoustic emission descriptors, such as activity during the unloading part of the cycles, provided the critical level of damage accumulation in the material. Acoustic emission allowed to closely follow the actual crack growth monitored by IR thermography, enabling quantitative measurements.
Smart Sensor Phenomena, Technology, Networks, and Systems 2011, 2011
Acoustic Emission (AE) supplies information on the fracturing behavior of different materials. In... more Acoustic Emission (AE) supplies information on the fracturing behavior of different materials. In this study, AE activity was recorded during fatigue experiments in metal CT specimens with a V-shape notch which were loaded in fatigue until final failure. AE parameters exhibit a sharp increase approximately 1000 cycles before than final failure. Therefore, the use of acoustic emission parameters is discussed both in terms of characterization of the damage mechanisms, as well as a tool for the prediction of ultimate life of the material under fatigue. Additionally, an innovative nondestructive methodology based on lock-in thermography is developed to determine the crack growth rate using thermographic mapping of the material undergoing fatigue. The thermographic results on the crack growth rate of aluminium alloys were then correlated with measurements obtained by the conventional compliance method, and found to be in agreement.
Smart Sensor Phenomena, Technology, Networks, and Systems 2011, 2011
ABSTRACT The purpose of this study is to develop an innovative non-destructive methodology for an... more ABSTRACT The purpose of this study is to develop an innovative non-destructive methodology for analyzing the thermal effects in metallic materials caused by fatigue. Mechanical stresses induced by cyclic loading in the material cause heat release due to microstructural changes, which results in an increase of the material's temperature. The heat release was quantified as a function of fatigue cycles in carbon steel samples. Mechanical hysteresis phenomena were analyzed to identify the metrics of damage, which relates to thermal parameters characterizing the level of damage of the material as a function of fatigue cycles.
Smart Sensor Phenomena, Technology, Networks, and Systems Integration 2012, 2012
ABSTRACT Composite materials are widely used especially in the aerospace structures and systems. ... more ABSTRACT Composite materials are widely used especially in the aerospace structures and systems. Therefore, inexpensive and efficient damage identification is crucial for the safe use and function of these structures. In these structures low-velocity impact is frequently the cause of damage, as it may even be induced during scheduled repair. Flaws caused by lowvelocity impact are dangerous as they may further develop to extended delaminations. For that purpose an effective inspection of defects and delaminations is necessary during the service life of the aerospace structures. Within the scope of this work, an innovative technique is developed based on current stimulating thermography. Electric current is injected to Carbon Fiber Reinforced Composite and aluminium (Al) plates with concurrent thermographic monitoring. For reference, both damaged and undamaged plates are inspected. Low-velocity impact damaged composite laminates at different energy levels are interrogated employing the novel technique. Live and pulse phase infrared thermography is employed for the identification of low-velocity impact damage at various energy levels while the electric current induces the transient thermal field in the vicinity of the defect. In all cases conventional ultrasonics (C-scan) were performed for the validation and assessment of the results of the innovative thermographic method.
ABSTRACT Acoustic emission (AE) supplies information on the fracturing behavior of different mate... more ABSTRACT Acoustic emission (AE) supplies information on the fracturing behavior of different materials. In this study, AE activity was recorded during fatigue experiments in metal coupons. The plates were characterized by a symmetric V-shape notch and were loaded in tension–tension fatigue until final failure with concurrent AE activity monitoring. The relatively broad bandwidth of the sensors enabled the recording of a wide range of frequencies up to 1MHz. AE parameters like energy and duration exhibited a certain increase with the accumulation of damage although the hit rate was not significantly influenced. Furthermore the behavior of RA value (ratio of rise time to amplitude of the waveforms) which quantifies the shape of the first part of the AE signals and has been used for characterization of the cracking mode, showed a certain shift indicating the transition from tensile mode to shear which can be confirmed by the visual observation of the crack geometry after the experiment. The time history of RA is similar to the crack propagation rate (da/dN) curve but exhibits the rapid hyperbolic growth consistently about 1000 cycles earlier than final failure. Therefore, the use of acoustic emission parameters is discussed both in terms of characterization of the damage mechanisms, as well as a tool for the prediction of ultimate life of the material under fatigue.
ABSTRACT Infrared thermography is a powerful non-destructive testing technique which can be used ... more ABSTRACT Infrared thermography is a powerful non-destructive testing technique which can be used for the detection of damage in advanced materials such as ceramic matrix composites. The purpose of this study is to apply a non-destructive methodology for analyzing, in real-time, the thermal effects in ceramic matrix composites caused by cyclic loading. Mechanical stresses induced by cyclic loading cause heat release in the composite due to failure of the interface, which results in increasing the material’s temperature. The heat waves, generated by the thermo-mechanical coupling, and the intrinsic energy dissipated during mechanical cyclic loading of the specimen, were detected by an infrared camera. The results were correlated with acoustic emission events that occurred during the damage accumulation process of the material.
Barium osumilite (BMAS) ceramic matrix composites reinforced with SiC-Tyranno fibers are tested i... more Barium osumilite (BMAS) ceramic matrix composites reinforced with SiC-Tyranno fibers are tested in a cyclic loading protocol. Broadband acoustic emission (AE) sensors are used for monitoring the occurrence of different possible damage mechanisms. Improved use of AE indices is proposed by excluding low-severity signals based on waveform parameters, rather than only threshold criteria. The application of such improvements enhances the accuracy of the indices as accumulated damage descriptors. RA-value, duration, and signal energy follow the extension cycles indicating moments of maximum or minimum strain, while the frequency content of the AE signals proves very sensitive to the pull-out mechanism.
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Papers by Evangelos Kordatos