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.
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: 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.
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.
Different measurement methodologies have been used in bridge monitoring due to seismic, environmental and operating loading. Moreover, bridge monitoring systems have influence in the smooth operation of the traffic load in big cities and thus it’s crucial to encourage monitoring techniques that are flexibly adaptable to various construction building models. Even though a lot of research has been performed in bridge health monitoring in order to identify damages or deterioration of the structural elements there is still a need for a method that could combine multisensor techniques in big data processing for multisource loading. The behavior of the cable-stay bridge model is being monitored via acoustic emission and 2D laser Doppler vibrometry systems. In each case, both static and dynamic loading conditions have been applied. The goal is to correlate the results of these nondestructive evaluation techniques during static and dynamic response of different support situations. The purpose of this work is to improve bridge design and enable the detection of distributed failures during a multifactor loading system.
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.
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.
Scanning acoustic microscopy uses a focused acoustic beam to investigate local elastic properties on the surface of a material. The measurement is based on the difference in propagation time between the direct reflection and the Rayleigh wave. This work deals with the development of a fully automated acoustic microscopy method in order to determine the near-surface elastic property and map sub-surface features in metallic and composite materials. This method allows for the detection and analysis of Rayleigh waves, which are sensitive to subtle changes in the material’s local elasticity. Via this process, the periodicity of the V(Z) curve can be initially assessed and the local Rayleigh velocity of the material is determined. In this work, the automated acoustic microscopy method was applied for the assessment of aluminum and Al-SiC metal matrix composites.
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.
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 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.
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.
The addition of a conductive admixture in a cement-based material could lead to innovative products with multifunctional features. These materials are designed to possess enhanced properties, such as improved mechanical properties, electrical and thermal conductivity, and piezo-electric characteristics. Carbon nanotubes (CNTs) can be used as nano-reinforcement in cement-based materials because of their huge aspect ratio as well as their extremely large specific surface area. For cement-based composites, one of the major types of environmental attack is the chloride ingress, which leads to corrosion of the material and, subsequently, to the reduction of strength and serviceability of the structure. A common method of preventing such deterioration is to avert chlorides from penetrating the structure. The penetration of the concrete by chloride ions is a slow process. It cannot be determined directly in a time frame that would be useful as a quality control measure. Therefore, in order to assess chloride penetration, a test method that accelerates the process is needed, to allow the determination of diffusion values in a reasonable time. In the present research, nanomodified mortars with various concentrations of multi-wall carbon nanotubes (0.2% wt. cement CNTs - 0.6% wt. cement CNTs) were used. The chloride penetration in these materials was monitored according to ASTM C1202 standard. This is known as the Coulomb test or Rapid Chloride Permeability Test (RCPT).
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.
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.
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