Smart packaging of food products is a new promising technology aiming to the preservation of consumer’s health and safety while prolonging the products’ self-life in transport and mass storage. Smart packaging can be applied by using chemical and/or biological sensors for monitoring indicators associated with bacterial growth and spoilage, as well as pathogen contamination. Poultry meat is a nutrient-rich matrix which supports the growth of various micro-organisms and the extended storage time can allow the proliferation of different microbial species on meat surfaces. The nature of the packaging approaches and storage factors can dictate the nature of the spoilage that transpires, with respect to the dominant microflora of the end-product. In the present study an innovative approach is explored for the development of cost-effective 3D-printed biosensors for monitoring known indicators associated with bacterial growth and spoilage in poultry meat. Spoilage was also independently measured using MSI and FT-IR spectroscopic methods. The development of a protocol for pathogen screening was also investigated with real-time polymerase chain reactions (qPCR).
The present study aims to accent the effect of nano-reinforcements such as CNTs and graphene nanoplatelets, on the electrical and thermal behavior of nano-modified concrete. The dispersion agent used is a water-based superplasticizer since this type of agent does not induce air in the specimens and is also chemically compatible. The assessment of the specimens includes evaluation of different physical properties, such as electrical resistivity and thermal behavior. The enhancement of these physical properties by the nano-reinforcement phase, induces multifunctionalities in the concrete specimens. Such innovative nano-reinforced concrete mixtures would enable the use of concrete in new areas like energy harvesting, real time health monitoring and self-sensing of critical structural elements.
Since wear and corrosion of materials currently causes large losses of GDP, surface engineering is a critical technology that currently supports the competitiveness of industry globally. Major sectors such as energy, aerospace, automotive and tool industries, are heavily dependent on surface treatments. It is estimated that almost 80% of all these industrial applications depend on protective coatings. Although different coatings have been developed in recent years, two types dominate the field of protective coatings, Hard Chrome and Cermet WC-Co coatings. Both types of coatings have very good mechanical and tribological properties, however, the extremely negative environmental impact of the hard chrome process related to the use of carcinogenic hexavalent chromium has led to a series of directives and legislation in several countries on limiting this method. Additionally, recent studies have shown that WC-Co particles are toxic in a dose and time-dependent manner. This was the driver for developing an innovative technology based on the incorporation of nanoparticles into the electrolytic deposition or thermal spray production line to create green protective nano-reinforced multifunctional coatings. The innovative green solution presented here is accompanied by significant benefits beyond their excellent performance. In particular, the new processes can be easily adopted combining flexibility with mass production, being environmentally friendly and nonharmful to health, combining low implementation costs with green footprint both in terms of materials and processes. Moreover, the novel coatings are being characterized with different destructive and nondestructive techniques and their performance is being compared with traditional coatings.
The main purpose of this work is the development of a novel nondestructive and non-contact method based on nonlinear acousticsfor assessing the structural integrity of metallic alloys. This method enables real-time monitoring of the material’s degradation. The introduction of a sinusoidal ultrasonic wave, of given frequency and sufficient amplitude into an anharmonic solid, leads to the distortion of the propagating wave. This results to the generation of higher harmonics of the fundamental frequency. In comparison with linear ultrasonic parameters, such as velocity and attenuation, the measurement of the amplitude of these harmonics provides information on the coefficient of higher order terms of the stress strain for the nonlinear solid. A metallic alloy subjected to cyclic loading accumulates damage with time resulting to large changes of the material’s nonlinear parameters. This paper deals with monitoring the second and third harmonics of metallic alloy specimens during mechanical fatigue using Laser Doppler Vibrometry (LDV). Surface acoustic waves were used to induce a single frequency ultrasonic wave in the material for in-situ characterization of the fatigue damage. The LDV technique was able to resolve the third harmonic enabling to assess the third order nonlinear parameter in addition to the second one. It was shown that the third order nonlinear parameter provides a very sensitive measurement of minute microstructural changes due to fatigue.
KEYWORDS: 3D modeling, Thermography, Thermal modeling, 3D scanning, Nondestructive evaluation, Cultural heritage, Scanners, Data modeling, Data fusion, 3D image processing
The authentication and sustainability of cultural heritage monuments are of great importance due to their uniqueness. Recent accidents and natural disasters have taught us that all monuments, even the most protected such as the cathedral Notre-Dame de Paris, can be destroyed by an unexpected event. For these reasons, it is of paramount importance the creation of a monument database containing fusion data not only of the accurate 3D model and precise representation of the artifacts/monuments but also about the condition and procedures of restoration and preservation and the structural health of the antiquities by means of quantitative non-destructive techniques, such as Infrared Thermography. The 3D model of a monument would guarantee the accurate restoration of the monument in case of a catastrophic disaster, while the 3D model of an artifact together with the entire related metadata would provide a digital identity, therefore guaranteeing the sustainability of the item. Also, in case of a movable artifact, it will be a useful tool towards the validation / authentication of the artifact in case it is damaged or missing.
Smart cement-based nano-reinforced structures have improved properties and are expected to remain intact for a long time. Corrosion attack, mainly through the pores, causes reduction of properties in most materials. Nano-reinforced structural components intended to be used in the construction industry require an understanding of their corrosion resistance behavior. The present work deals with the investigation of chloride penetration mechanisms in mortars modified with multi-walled carbon nanotubes. The tested structures were artificially corroded via salt spray fog and their surface electrical resistivity, as well as their flexural and compressive strengths were assessed. One of the main goals of the study is to evaluate the effect of nanotube concentration on the accelerated corrosion damage. It was observed that the insertion of different percentages of carbon nanotubes affects the mortar chloride penetration, as well as enhances the flexural and compressive response of the material, comparing to plain specimens, due to the filling of pores with sodium chloride. Also, the electrical resistivity of the specimens was evaluated prior and after the exposure of the mortar samples to salt spray fog.
KEYWORDS: Sensors, Safety, Packaging, Aerosols, Chemical analysis, Printing, Inkjet technology, Chemical elements, Biological and chemical sensing, Transducers
The packaging of agricultural products is of paramount importance for managing the food supply with innovative and safe products. The consumer, at the same time, is increasingly aware of the impact of packaging on the environment ensuring that the value of packaged agri-food products depends on the threefold control, quality, protection. The present study reveals new possibilities that cover (a) food safety and traceability by applying smart packaging solutions, and (b) ensuring and verifying the authenticity of packaged agri-food products. The innovative sensors and procedures which are being developed enable novel intelligent traceability systems aiming to provide product quality and safety information to effectively control the supply chain and predict the remaining shelf-life of the product. To this end, low-cost, batteryless wireless interdigital sensing systems equipped with two-way response antenna, have been directly deposited on packages made of any material or shape, having the possibility of integrating in real-time with packaged agri-food products. Also, new methodologies are being developed, aiming to verify food authenticity leading to the protection of the consumer from fraud, counterfeiting or improper packaging of protected designation of origin products such as dairy products, olive oil, as well as herbs and spices.
It is well known that the behavior and properties of construction materials largely rely on the characteristics of their internal microstructure. It is important the curing process in freshly poured cementitious materials to be understood to successfully carry out every stage of construction development. Shortly after the mixing procedure, at the state when the suspension transmutes from the liquid to the solid-state phase, the ultrasonic wave propagation and the low pulse velocity of cement-based materials exhibit simultaneously a significant decrease. This is followed by an increase in both the ultrasonic pulse velocity and the signal amplitude. The point of solidification is responsible for the load-bearing capacity of the cement composite and its long-term behavior. At the point of phase change which occurs during curing, the nonlinear behavior of the material exhibits a notable sensitivity. This work aims at the comparison between nano-enhanced and plain cement-based composites regarding their hydration process. Multi-walled carbon nanotubes (MWCNTs) have been used as nano-enhancement in the cement paste specimens. The MWCNTs were synthesized via catalytic chemical vapor deposition, while a water-based superplasticizer was selected as the dispersion agent. The early stages of freshly poured materials were monitored using nonlinear elastic waves. A contact ultrasonic transducer and a noncontact optical detection device (Laser Doppler Vibrometer) were used for the experimental measurements. This method assesses the amplitudes of harmonic vibrations of an elastic wave with a specific fundamental frequency, propagating through the material, leading to the evaluation of its internal structure.
Constructions filled with carbon-based additives are intended to be the next-generation multifunctional materials with advanced mechanical capabilities and ideal smart strain sensing characteristics. Such additives are the graphene nanoplatelets that represent a new class of carbon nanoparticles/nanopowder and consist of small stacks of graphene sheets with an overall thickness of approximately 3-10 nanometers. Their unique size and platelet's morphology make these particles effective at providing barrier characteristics to the supreme applications that are used. The present study has as aim to report on the effect of graphene nanoplatelets presence on mechanical and electrical behavior as well as on the fracture mode of graphene nano-modified cementitious mortars. Pure bending, compression, and fracture tests with the simultaneous acoustic emission monitoring were carried out on specimens fabricated by the introduction of 0 to 1.2 wt. % pure few-layer graphene nanoplatelets in the different mixtures. A suspension for every graphene loading was produced under the ultrasonication procedure. A water-based superplasticizer was selected as dispersion agent based on its efficiency in inhibiting air entrapment inside the specimens and on its chemical stability. As concern the graphene-enhanced mortars the great improvements in mechanical characteristics and also the notable differences in fracture energy of specimens were documented at specific graphene loadings; the improvement was assessed simultaneously by acoustic emission data. In addition, the electrical response of the graphene-modified cement mortars, via the electrical conductivity measurements, is another property that was studied, and the total results are presented and discussed in the present paper.
This study aims in developing an advanced 3d digitization and nondestructive evaluation methodology that will serve as a baseline to advanced Augmented Reality (AR) and Virtual Reality (VR) applications of sites with archaeological interest in order to enhance not only the on-site experience for the visitors and the visitors via internet but as well to provide a useful tool for the preservatives, through improved supervision processes during maintenance. To this regard, a consolidated database is being created by the use of the best combination of state-of-the-art techniques of 3D digitization not only of the archaeological site itself but also of archaeological findings that at this time are presented in the museum. All the aforementioned data, created a database of the monument that aims to provide an augmented and virtual experience which is beyond the state of the art not only to the visitors but also to the preservative teams and it will help definitely towards the sustainability of the monument.
An essential issue in materials research, quality control, and in practical planning and implementation of construction projects, is the understanding of the curing process of fresh cement-based materials. Immediately after mixing, cementitious materials exhibit a significant damping effect on ultrasonic wave propagation together with low pulse velocity. During the curing process, ultrasonic waves, especially the nonlinear acoustic behavior of the material, are sensitive to the point at which the solid phase appears. After this point, the ultrasonic pulse velocities and signal amplitudes increase continuously. The point of solidification is of practical significance since the connectivity of the solid phase is responsible for the load-bearing capacity of the cement composite and its long-term behavior. The aim of this study is to monitor the early stages of fresh cement-paste composites during the hydration process using nonlinear elastic waves. The measurements in this work were performed using a combination of contact ultrasonic transducer and noncontact optical detection measurement device. The principle of operation of the detection device is based on the doppler effect. Using this technique, the amplitudes of harmonic vibrations of an elastic wave with a fundamental frequency propagating through the material can be assessed. This leads to the evaluation of important materials characteristics, such as the changes in internal microstructure of fresh concrete during curing, the evolution of higher order elastic contants of the material expressed in the form of nonlinear parameters, as well as the longitudinal wave velocity.
One of the most common methods of surface treatment of the aluminum is anodizing, which improves several metal properties (mechanical, electrical, magnetic, optical, etc.) as well as corrosion resistance. The aim of this work was to investigate the ability of this oxide to protect the tested material from corrosion and its response under the mechanical cyclic loading. In the present study, specimens of Al 1050-H16 were surface anodized at constant voltage using sulfuric acid solution and a layer of aluminum oxide is produced on the surface of the specimen. The anodized specimens were subjected to a corrosive environment simulating the physical exposure to seawater and their subsequent mechanical stress by fatigue method. Two complementary nondestructive evaluation methods, infrared thermography and acoustic emission, were used for predicting the material's fatigue life. The results of the tests of the anodized specimens with and without corrosion were compared with each other, as well as with the corresponding data of the same materials without any treatment. In addition, white light interferometry was used for profiling observation of the aluminum samples in order to characterize the effect of the corrosion process on the specimens’ surface.
Infrared thermography (IRT) is a well-established and well-documented nondestructive evaluation (NDE) technique which has been proved as one of the critical assessment tools providing not only qualitative but also quantitative results useful for various applications. Even though many post processing methodologies have been used for thermal imaging analysis, there is still a need for a methodology that could possibly reduce the noise, improve the Signal to Noise Ratio (SNR) and focus on a specific area of interest reconstructing automatically the thermal image. This work deals with fine-tuning the IRT method in order to assess the detectability of damage in composite materials.
This work aims to develop a nondestructive technique based on Near Infrared (NIR) imaging for the evaluation of transparent and semi-transparent composite materials, such as Glass Fiber Reinforced Polymers (GFRP) and laminated glass aircraft components. The NIR technique offers enhanced optical imaging of damage which cannot be detected with conventional optical inspection. The NIR imaging can be performed in reflection or transition mode (i.e. radiation reflected from or transmitted through an object under inspection). While the NIR transmission mode is better for detecting deeper defects, it has a serious limitation for field application in real aircraft parts, since it requires simultaneous access (e.g. illumination source, cabling, etc.) of both sides of the structure. For these reasons, an innovative NIR approach, the NIR Double-Transmission Mode (NIR-DTM), has been developed. The new approach is based on the advantages of both aforementioned techniques while eliminating their deficiencies. In order to optimize the use of NIR imaging for field applications, different parameters that affect the operation of the technique were considered. These parameters include the surface geometry, the distance from the material under investigation, the inspection angle, as well as the type and intensity of excitation source. Finally, image processing and analysis tools were used to improve the inspection sensitivity and further decrease the inspection time.
This work deals with the study of the fatigue behavior of metallic materials for aerospace applications which have undergone erosion. Particularly, an innovative non-destructive methodology based on infrared lock-in thermography was applied on aluminum samples for the rapid determination of their fatigue limit. The effect of erosion on the structural integrity of materials can lead to a catastrophic failure and therefore an efficient assessment of the fatigue behavior is of high importance. Infrared thermography (IRT) as a non-destructive, non-contact, real time and full field method can be employed in order the fatigue limit to be rapidly determined. The basic principle of this method is the detection and monitoring of the intrinsically dissipated energy due to the cyclic fatigue loading. This methodology was successfully applied on both eroded and non-eroded aluminum specimens in order the severity of erosion to be evaluated.
In recent years, the damage assessment by means of Laser Doppler Vibrometry (LDV) has become very attractive as it provides non-contact, non-destructive, accurate and improved evaluation of advanced materials. This study deals with the development of advanced software based on LabVIEW in order accurate and automated measurements of acoustic activity to be achieved. Furthermore, this automated method was applied for damage detection in aluminum 1050 Η16 undergone cyclic mechanical loading. LDV was used to measure the amplitude of a Rayleigh surface wave propagating in aluminium specimens. Rayleigh waves are experimentally generated with a piezoelectric transducer and detected by LDV. The proposed measurement technique is used to assess the damage and its evolution, in terms of the increasing amplitude of Rayleigh wave, in 1050 H16 specimens under cyclic mechanical loading. In addition, the reduction in the Rayleigh wave velocity it depends on ultimate fatigue strength of material. The development of this process allows the automated, improved and detailed damage assessment of composite materials.
Today’s electronics industry, due its continues growth and increasing demand for devices such as cell phones, satellite navigation systems, health devices, etc., faces important challenges related to the vast quantity of raw materials needed for sustainability and the quantity of waste generated from electronics equipment. To sustain its growth, the electronics industry needs innovations, such as the miniaturization of printed circuit boards (PCB) for increasing components density. Consequent development of miniaturized electronics design plays, therefore, a key role for the reduction of energy consumption and raw materials sustainable use. A factor, however, that currently limits this endeavor is the availability of hyperfine pitch solder powder pastes. The present work focuses on the development of novel, low cost, type 8 and 9 solder pastes with hyperfine solder particles (with size distribution of 1-10 μm) aiming at printing PCBs with increased component density. The solder joint quality was characterized using nondestructive techniques after manufacturing at different reflow parameters. Infrared thermography and white light interference microscopy provided information on internal defects such as presence of micro-voids, as well as on the topography of geometrical variations of solderbals, solder errors, and warpage of components, which are related to the thermal history of the component during reflow.
One of the important characteristics of metallic structures affecting structural integrity is their behavior in corrosive environment. In this respect, aircraft components made from aluminum alloys can catastrophically fail due to pitting corrosion and fatigue damage. Pitting, because of stress concentration, is responsible for fatigue crack nucleation in the material. In the current study, tensile-shape samples of aluminum alloy are immersed in NaCl solution, which simulates the natural exposure in a marine environment. This has an objective to induce accelerated electrochemical damage of the material under testing by the controlled pitting corrosion in a specific area of the surface using different electrochemical techniques, while the rest of the specimen remains completely sealed. In order to investigate the effect of pitting corrosion on the degradation of the material’s mechanical performance, the specimens were subjected to cyclic loading. The corrosion fatigue testing results were compared to data obtained from the uncorroded materials. Using a scanning white-light interferometer the pits' morphology was characterized and the effect of corrosion on the fatigue life was assessed. The results were validated using two complimentary nondestructive techniques, namely infrared thermography and acoustic emission.
This work deals with the development of a prototype infrared sensor and infrared thermography (IRT) approach for nondestructive testing of aerospace materials and components. Thermography offers noncontact, wide area detection of subsurface defects, and can be used as an alternative or complement to conventional inspection technologies. The novel approach is based on the combination of Pulsed Phase Thermography (PPT) and Lock-in Thermography (LT). The technique provides with initial fast qualitative information of defects by the PPT technique such as location, approximate dimensions and depth of the defect, as well as an indication of the frequency range over which the LT technique would subsequently be applied for obtaining accurate quantitative characterization of the damage. The new IR approach enables fast inspection as well as qualitative and quantitative results such as the size, type and depth of defects.
This work focuses on the development of novel nano-reinforced composite protective coatings for a wide range of applications, such as aerospace, automotive, energy and cutting tools industries. In the present work, silicon carbide (SiC) nanoparticles of 100nm and purity of 99% were used to form nickel-high phosphorus matrix composite (Ni–P– SiC) coatings on steel plates, which were prepared by direct current electrodeposition with duty cycle values of 50% and 80%, while the frequency of the imposed pulses was varied between 0.1Hz and 100Hz. Nickel sulphate served as the primary Ni source, while nickel chloride was added to improve anode corrosion, solution conductivity, and uniformity of the coating thickness distribution. Phosphorous acid acted as the P source in the solution and H3BO3 was added as buffering agent. Sodium dodecyl sulphate has been used as a wetting agent, and saccharin as a stress reducing additive. XRD characterization showed that the structure of NiP composite coatings as deposited were amorphous, irrespective of the presence of SiC. After heat treatment at 400°C for one hour, the amorphous phase was crystallized at steady phases of Ni and Ni3P. The morphology and structure as well as the elastic property of the coatings with and without the SiC nanoparticles were assessed using infrared thermography and scanning acoustic microscopy.
Cement matrix composites with a conductive nano-reinforcement phase, lead to the development of innovative products. A matrix with carbon based nano-inclusions (graphene, carbon nanotubes, carbon nanofibers, carbon black) obtains multi-functional properties like enhanced mechanical, electrical, elastic and thermal properties and, therefore, the advantage of self-sensing in case of an inner defect. This research aims to characterize the nano-modified cement mortars with different concentrations of graphene nanophase. The results will be compared with data obtained from nanomaterials containing multi-walled carbon nanotubes. Comprehensive characteristics of these cement-based nanocomposites have been determined using destructive and nondestructive laboratory techniques. Flexural and compressive strength were measured. During four point bending tests, acoustic emission monitoring allowed for realtime identification of the damage process in the material. The electrical surface resistivity of graphene-reinforced cement mortars was measured by applying a known DC voltage, and compared to the electrical resistivity of nano-modified mortars with carbon nanotubes.
In this work the influence of the microstructure at the vicinity of the interface on the fracture behavior of particulate-reinforced aluminum alloy matrix composites (Al/SiCp composites) is studied by using thermographic tools. In particular, infrared thermography was used to monitor the plane crack propagation behavior of the materials. The deformation of solid materials is almost always accompanied by heat release. When the material becomes deformed or is damaged and fractured, a part of the energy necessary to initiate and propagate the damage is transformed in an irreversible way into heat. The thermal camera detects the heat wave, generated by the thermo-mechanical coupling and the intrinsic dissipated energy during mechanical loading of the sample. By using an adapted detector, thermography records the two dimensional "temperature" field as it results from the infrared radiation emitted by the object. The principal advantage of infrared thermography is its noncontact, non-destructive character. This methodology is being applied to characterise the fracture behavior of the particulate composites. Infrared thermography is being used to monitor the plane crack propagation behavior of such materials. Furthermore, an innovative approach to use microscopic measurements using IR microscopic lenses was attempted, in order to enable smaller features (in the micro scale) to be imaged with accuracy and assurance.
This paper deals with the use of complimentary nondestructive methods for the evaluation of damage in engineering materials. The application of digital image correlation (DIC) to engineering materials is a useful tool for accurate, noncontact strain measurement. DIC is a 2D, full-field optical analysis technique based on gray-value digital images to measure deformation, vibration and strain a vast variety of materials. In addition, this technique can be applied from very small to large testing areas and can be used for various tests such as tensile, torsion and bending under static or dynamic loading. In this study, DIC results are benchmarked with other nondestructive techniques such as acoustic emission for damage localization and fracture mode evaluation, and IR thermography for stress field visualization and assessment. The combined use of these three nondestructive methods enables the characterization and classification of damage in materials and structures.
The present work deals with the nondestructive assessment of the metallic materials’ mechanical damage. An innovative Nondestructive Evaluation (NDE) methodology based on two thermographic approaches was developed in order the state of fatigue damage to be assessed. The first approach allows the detection of heat waves generated by the thermomechanical coupling during the fatigue loading (online method). Specifically, both the thermo-elastic and intrinsic dissipated energy was correlated with the mechanical degradation and the remaining fatigue life. The second approach involves the monitoring of the materials’ thermal behavior using a Peltier device for accurate thermal excitation (offline method). The correlation of the thermal behavior and the state of damage was achieved by the determination of the material’s thermal response. The combination of these two approaches enables the rapid and accurate assessment of the cumulative damage.
The corrosion behavior of metallic structures is an important factor of material performance. In case of aluminum matrix composites corrosion occurs via electrochemical reactions at the interface between the metallic matrix and the reinforcement. The corrosion rate is determined by equilibrium between two opposing electrochemical reactions, the anodic and the cathodic. When these two reactions are in equilibrium, the flow of electrons from each reaction type is balanced, and no net electron flow occurs. In the present study, aluminum alloy tensile-shape samples are immersed in NaCl solution with an objective to study the effect of the controlled pitting corrosion in a specific area. The rest of the material is completely sealed. In order to investigate the effect of pitting corrosion on the material performance, the specimens were subjected to cyclic loading. The effect of corrosion on the fatigue life was assessed using two complimentary nondestructive methods, infrared thermography and acoustic emission.
This work deals with the development of a new class of metamaterials based on phononic composite structures that can offer vibration protection in a wide range of applications. Such phononic heterostructures is a class of phononic crystals that exhibit spectral gaps with lattice constants of a few orders of magnitude smaller than the relevant acoustic wavelength. The design of a phononic composite metamaterial is based on the formation of omnidirectional frequency gaps. This is very much relevant to the dimensionality of a finite slab of the crystal. In this respect, two dimensional structures are used to cut off acoustic waves. In this study, different infrared thermography techniques were used in order to assess the phononic structure’s geometry, as well as to determine the thermal properties of the metamaterial.
A full elastodynamic multiple scattering approach is employed to investigate the behavior of nonreciprocal phononic structures consisting of periodic helical assemblies of spheres. We report on cases of dense and sparse helical chains, cases with size variation and low frequency behavior.
This research aims to investigate the influence of the nano-reinforcement on the thermal properties of cement mortar.
Nano-modified cement mortar with carbon nanotubes (CNTs) leading to the development of innovative materials
possessing multi-functionality and smartness. Such multifunctional properties include enhanced mechanical behavior,
electrical and thermal conductivity, and piezo-electric characteristics. The assessment of the thermal behavior was
evaluated using IR Thermography. Two different thermographic techniques are used to monitor the influence of the
nano-reinforcement. To eliminate any extrinsic effects (e.g. humidity) the specimens were dried in an oven before
testing. The electrical resistivity was measured with a contact test method using a custom made apparatus and applying a
known D.C. voltage. This study indicate that the CNTs nano-reinforcement enhance the thermal and electrical properties
and demonstrate them useful as sensors in a wide variety of applications.
Cement-based materials have in general low electrical conductivity. Electrical conductivity is the measure of the ability of the material to resist the passage of electrical current. The addition of a conductive admixture such as Multi-Walled Carbon Nanotubes (MWCNTs) in a cement-based material increases the conductivity of the structure. This research aims to characterize nano-modified cement mortars with MWCNT reinforcements. Such nano-composites would possess smartness and multi-functionality. Multifunctional properties include electrical, thermal and piezo-electric characteristics. One of these properties, the electrical conductivity, was measured using a custom made apparatus that allows application of known D.C. voltage on the nano-composite. In this study, the influence of different surfactants/plasticizers on CNT nano-modified cement mortar specimens with various concentrations of CNTs (0.2% wt. cement CNTs - 0.8% wt. cement CNTs) on the electrical conductivity is assessed.
Current work deals with the non-destructive evaluation (NDE) of the fatigue behavior of metal matrix composites (MMCs) materials using Infrared Thermography (IRT) and Acoustic Emission (AE). AE monitoring was employed to record a wide spectrum of cracking events enabling the characterization of the severity of fracture in relation to the applied load. IR thermography as a non-destructive, real-time and non-contact technique, allows the detection of heat waves generated by the thermo-mechanical coupling during mechanical loading of the sample. In this study an IR methodology, based on the monitoring of the intrinsically dissipated energy, was applied for the determination of the fatigue limit of A359/SiCp composites. The thermographic monitoring is in agreement with the AE results enabling the reliable monitoring of the MMCs’ fatigue behavior.
The present paper describes the acoustic emission (AE) behavior and the mechanical properties of Portlant cement-based mortars due to the addition of multi wall carbon nanotubes (MWCNTs). This research aims in investigating the crack growth behavior of modified cement mortar with MWCNTs that act as nanoreinforcement during an unaxial compression test using acoustic emission technique. MWCNTs were used in various concentrations inside the matrix. Density, sound's speed, modulus, bending strength, compression strength were studied for five different concentrations. The adding and the increase of MWCNTs concentrations upper to 0.2 % by weight of cement not improving the mechanical properties of cement-based mortar but increase the acoustic emission activity.
The objective of the present study was the repair monitoring of an extensively cracked concrete floor using the Impulse – Response method. The study included the evaluation of the condition of the concrete floor that suffered from extensive cracking on its surface, through systematic tests. The purpose of the study was to investigate the causes that led to extensive cracking on the floor surface in order to plan the repair strategy. The investigation included a thorough visual inspection and recording of cracks, estimation of the crack depth using ultrasonic pulse velocity measurements, investigation for voids between the concrete floor and the underlying aggregate layer using the Impulse – Response method, concrete floor thickness estimation using the Impact – Echo method and concrete quality estimation using cores cutting. The repair method that was chosen was based on grout injections in order to fill the voids located between the concrete and the underlying aggregate layer. The area, where the injections took place, was inspected using the Impulse – Response method before and after the injections for monitoring purposes and a secondary grid was designed after considering the results. The area was inspected for a third time, after injecting in the secondary grid, in order to confirm the successful filling of the voids.
This research aims in characterizing modified cement mortar with carbon nanotubes (CNTs) that act as nanoreinforcements
leading to the development of innovative materials possessing multi-functionality and smartness. Such
multifunctional properties include enhanced mechanical behavior, electrical and thermal conductivity, and piezo-electric
characteristics. The effective thermal properties of the modified nano-composites were evaluated using IR
Thermography. The electrical resistivity was measured with a contact test method using a custom made apparatus and
applying a known D.C. voltage. To eliminate any polarization effects the specimens were dried in an oven before testing.
In this work, the thermal and electrical properties of the nano-modified materials were studied by nondestructively
monitoring their structural integrity in real time using the intrinsic multi-functional properties of the material as damage
sensors.
In the present work, a novel method of infrared (IR) thermography called Thermo - Electrical
Lockin Thermography (TELT) was developed for the characterization of subsurface defects in
materials and structures. This new IR thermography method is based on the thermal excitation of
materials under testing using a Peltier device and appropriate electronics allowing for accurate
thermal cycling. Results from using this method were compared with different IR methodologies
(i.e. Pulsed Phase thermography). It was found that Thermo - Electrical Lockin Thermography
provides not only qualitative but also quantitative results.
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.
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