FUCILE DA PESCA SUBACQUEO A DUE FUSTI ORIZZONTALI CON ASTA SINGOLA O DOPPIA

Il brevetto ha per oggetto un fucile subacqueo caratterizzato da due aste, o arpioni, indipendenti che possono essere sparate separatamente. Un’altra variante dell’invenzione prevede una singola asta. Il brevetto presenta numerosi innovazioni che si traducono in significativi vantaggi funzionali rispetto ai fucili subacquei ad elastico attualmente sul mercato. Oltre ai numerosi benefici derivanti dalla possibilità del doppio sparo, lo schema costruttivo azzera le deformazioni dovute al carico esercitato dagli elastici in tensione di cui soffrono i tradizionali fucili subacquei ad elastico, ne consegue una elevata precisione del tiro anche con fusti di piccolo diametro, molto idrodinamici, r…

Dispositivo di smorzamento del rollio per imbarcazioni all’ancora o alla deriva con motori spenti

La presente invenzione si riferisce ad un nuovo dispositivo di smorzamento del rollio, inseribile e disinseribile, per imbarcazioni all’ancora o alla deriva con motori spenti. Novel roll damping device for a vessel, in particular when the vessel is anchored or drifting with the engines off

Modello numerico per la simulazione e l’ottimizzazione di controlli non distruttivi con ultrasuoni

I controlli non distruttivi basati sull’impiego di ultrasuoni sono ampiamente usati per la loro efficacia e affidabilità nel rilevamento di difetti. La generazione di onde ultrasonore e la propagazione in strutture di forma non regolare sono difficili da analizzare, soprattutto se la sorgente impiegata è un laser. Le tecniche numeriche per la simulazione del fenomeno reperibili in letteratura mostrano limiti di applicabilità per frequenze nel campo dei MHz e lunghezze d’onda molto corte. In questo lavoro presentiamo un metodo numerico in grado di risolvere accuratamente ed efficientemente problemi di generazione di onde ultrasonore tramite laser, con frequenze nel range dei MHz, e di propag…

A Penalty-Based Interface Technology for Coupling Independently Modeled Three-Dimensional Finite Element Meshes

An effective and robust 2D interface element able to connect independently modeled 3D finite element subdomains is presented. This method has been developed using a hybrid variational formulation with the penalty constraints. which leads to a computational approach that is very efficient. A significant effort has been directed toward developing an automatic calculation of the proper penalty parameter for each interface constraint. This paper extends the previous work on the 1D penalty-based interface element for connecting 2D meshes. A variety of 3D problems have been investigated to validate the formulation.

Electronic properties of carbon nanotubes under torsion

A computationally-effective approach for calculating the electromechanical behavior of SWNTs and MWNTs of the dimensions used in nano-electronic devices has been developed. It is a mixed finite element-tight-binding code carefully designed to realize significant time saving in calculating deformation-induced changes in electrical transport properties of the nanotubes. The effect of the MWNT diameter and chirality on the conductance after mechanical deformation was investigated. In case of torsional deformation results revealed the conductance of MWNTs to depend strongly on the diameter, since bigger MWNTs reach much earlier the buckling load under torsion their electrical conductivity chang…

Electrical conductance of carbon nanotubes with misaligned ends

During a manufacturing process, when a straight carbon nanotube is placed on a substrate, e.g., production of transistors, its two ends are often misaligned. In this study, we investigate the effects of multiwall carbon nanotubes’ (MWCNTs) outer diameter and chirality on the change in conductance due to misalignment of the two ends. The length of the studied MWCNTs was 120 nm, while the diameters ranged between 4 and 7 nm. A mixed finite element-tight-binding approach was carefully designed to realize reduction in computational time by orders of magnitude in calculating the deformation-induced changes in the electrical transport properties of the nanotubes. Numerical results suggest that ar…

Carbon nanotube - Polymer Composites and their applications

Continuous Microfiber Wire Mandrel‐Less Biofabrication for Soft Tissue Engineering Applications

Suture materials are the most common bioimplants in surgical and clinical practice, playing a crucial role in wound healing and tendon and ligament repair. Despite the assortment available on the market, sutures are still affected by significant disadvantages, including failure in mimicking the mechanical properties of the tissue, excessive fibrosis, and inflammation. This study introduces a mandrel-less electrodeposition apparatus to fabricate continuous microfiber wires of indefinite length. The mandrel-less biofabrication produces wires, potentially used as medical fibers, with different microfiber bundles, that imitate the hierarchical organization of native tissues, and tailored mechan…

DISPOSITIVO PER RIFLETTERE LA LUCE SOLARE

La presente invenzione si riferisce ad un dispositivo per riflettere la luce solare, e ad un eliostato comprendente tale dispositivo. The present invention relates to a device for reflecting the solar light, and to a heliostat comprising such a device.

Nonlinear Structural Mechanics Based Modeling of Carbon Nanotube Deformation

A nonlinear structural mechanics based approach for modeling the structure and the deformation of single-wall and multiwall carbon nanotubes (CNTs) is presented. Individual tubes are modeled using shell finite elements, where a specific pairing of elastic properties and mechanical thickness of the tube wall is identified to enable successful modeling with shell theory. The effects of van der Waals forces are simulated with special interaction elements. This new CNT modeling approach is verified by comparison with molecular dynamics simulations and high-resolution micrographs available in the literature. The mechanics of wrinkling of multiwall CNTs are studied, demonstrating the role of the …

Stress Transfer within CNT Fibres: A FEA Approach

Abstract Carbon nanotube (CNT) fibres are characterized by extreme anisotropy in their structure and physical properties. These fibres have been shown to have high axial strength, but poor shear strength between carbon nanotubes; for this reason it is difficult to transfer stress uniformly acrossthe fibre cross section. Here, Finite Element Analysis (FEA) is used to predict the stress distribution and the stress-strain curves of CNT fibres. The resultsdemonstrate that, in accordance with St. Venant principle,very considerable length-to-diameter ratios (> 10 3 ) are required to obtain a uniform stress distribution within the fibres even in the presence of low applied strain.

Design of a Low Cost 3D Printable Single-Component Compliant Mechanism for FWMAV’s Wing Actuation

Considering a modern approach to design, one of the viable options for developing innovative projects is the possibility of integrating the effectiveness of the solutions offered by nature and living beings with the latest design methods. With this in mind, the following research exploits the idea of reproducing the natural flexibility inherent in biological structures by combining the advantages of compliant mechanisms with the adaptability of additive manufacturing processes. In the specific, the authors intend to highlight the potential and critical aspects of a possible approach for the application of compliant mechanisms in the development of single-component structures suitable for th…

Electrical Properties of Single and Multiwall Carbon Nanotubes Under Mechanical Deformations

Numerical–Analytical Model for Nanotube‐Reinforced Nanocomposites

Testing the Dispersion of Nanoparticles in a Nanocomposite with an Ultra-Low Fill Content Using a Novel Non-Destructive Evaluation Technique

A non-destructive evaluation (NDE) technique capable of testing the dispersion of nanoparticles in a nanocomposite would be of great use to the industry to check the quality of the products made and to ensure compliance with their specifications. Very few NDE techniques found in the literature can evaluate the level of dispersion of the nanoparticles in the whole nanocomposite. Here, a recently developed NDE technique based on pulsed phase thermography (PPT) in transmission mode was used to assess the particle dispersion in ultra-low, less than 0.05 wt%, Ag enriched polymeric based nanocomposite manufactured with an innovative nano-coating fragmentation technique. The phasegrams obtained wi…

Direct Simulation of Electronic Transport through Deformed Single and Multiwall Carbon Nanotubes. NANOMEC-06 Materials Science and Materials Mechanics at the Nanoscale,

Simulazione di propagazione di onde ultrasonore con applicazione ai controlli non distruttivi

I metodi di controllo ad ultrasuoni sono noti per essere efficaci ed affidabili per il rilevamento di difetti. L'uso del laser nei sistemi di controllo ad ultrasuoni consente l'ispezione remota, realizzabile in dinamico e automatizzabile. Inoltre, poiché le onde acustiche generate con il laser sono nel campo dei MHz, si ha una buona risoluzione spaziale per il rilievo di difetti. La propagazione di onde ultrasonore generate tramite laser in strutture di forma non regolare è un fenomeno difficile da analizzare. Le tecniche numeriche reperibili in letteratura mostrano limiti di applicabilità per frequenze nel campo dei MHz e lunghezze d’onda molto corte. In questo lavoro presentiamo un metodo…

Mechanics of carbon nanotube reinforced nanocomposites

Many numerical models have been developed in attempts to improve the understanding of the stiffening effects of CNTs in a polymer matrix. These studies are based on the micromechanical models, because the atomistic models are computationally too expensive to simulate the behavior of the composite. We emphasize that the majority of these continuum micromechanical models either explicitly or effectively adopt an assumption of an ideally-bonded interface between the compliant polymer matrix and the stiff CNTs, and often lead to predictions of overall composite stiffness that are quite optimistic compared to experimental results. Here the effects of waviness, diameter and volume fraction of CNT…

Carbon Nanotubes Dispersion Assessment in Nanocomposites by Means of a Pulsed Thermographic Approach

The extensive production of polymer composites reinforced by carbon nanotube is limited by the absence of non-destructive evaluation (NDE) methods capable of assessing product quality to guarantee compliance with specifications. It is well known that the level of dispersion of carbon nanotubes (CNTs) in the polymer matrix is the parameter that, much more than others, can influence their enhancement capabilities. Here an active Infrared Thermography Non Destructive Testing(IR-NDT) inspection, joined with pulsed phase thermography (PPT), were applied for the first time to epoxy-CNT composites to evaluate the level of dispersion of the nanoparticles. The PPT approach was tested on three groups…

Effects of curvature of the Carbon Nanotubes and Carbon Nanotube/matrix bonding on Nanocomposite stiffness

MIXED FINITE ELEMENT-TIGHT BINDING TECHNIQUE FOR STUDYING THE ELECTROMECHANICAL BEHAVIOR OF SINGLE AND MULTIWALL CARBON NANOTUBES

Inspection of additive-manufactured layered components

Laser powder deposition (LPD) is a rapid additive manufacturing process to produce, layer upon layer, 3D geometries or to repair high-value components. Currently there is no nondestructive technique that can guarantee absence of flaws in LPD products during manufacturing. In this paper a laser ultrasonic technique for in-line inspection of LPD components is proposed. Reference samples were manufactured from Inconel and machined flaws were created to establish the sensitivity of the technique. Numerical models of laser-generated ultrasonic waves have been created to gain a deeper understanding of physics, to optimize the set-up and to verify the experimental measurements. Results obtained on…

Guided Wave Propagation in a Plate Edge and Application to NDI of Rail Base

The analysis of guided wave propagation in a plate edge can be useful for some applications, such as for the inspection of the rail base. Here guided waves generated by a laser beam hitting, on the inclined surface, a solid media with trapezoidal cross-section have been studied. We have found that, for the geometry investigated, two guided waves propagate along both free surfaces of the plate, with same velocity and frequency. The analysis of the trajectories of the two material points, due to waves propagation, shows that the wave packets can be identified as Rayleigh waves. The presence of S0 Lamb mode, with low frequency and low amplitude, has been revealed too. As an example of a possib…

Palo telescopico per produzione eolica con ridotto impatto ambientale

Tra il 2015 e il 2016 un consorzio costituito da differenti partner ha sviluppato un progetto di ricerca per la realizzazione di un prototipo di un palo telescopico per produzione eolica con ridotto impatto ambientale ed il relativo sistema di sollevamento per una turbina di potenza da 60 a 250 kW e un’altezza di 30 m. Un palo eolico telescopico, che si solleva e si abbassa mediante automatismi o mediante controllo remoto, consente di differenziare nel tempo la presenza dell’aerogeneratore all’interno del paesaggio. La tecnologia attualmente disponibile per la movimentazione assiale dei pali eolici è applicabile a infrastrutture con altezze inferiori ai 10 metri e a pali ribaltabili di alte…

Influence of laser beam profile on the generation of ultrasonic waves

The different ultrasonic fields generated in metallic materials by a laser beam with flat and Gaussian profile are investigated experimentally and using the finite element method (FEM). A high power laser beam irradiating a solid surface produces elastic waves with a mechanics that depends on many parameters, including the profile of the laser beam. The influence of the beam profile is investigated with the FEM analysis, considering the temperature dependence of material properties.

Simulation of laser generated ultrasound with application to defect detection

Laser generated ultrasound holds substantial promise for use as a tool for defect detection in remote inspection thanks to its ability to produce frequencies in the MHz range, enabling fine spatial resolution of defects. Despite the potential impact of laser generated ultrasound in many areas of science and industry, robust tools for studying the phenomenon are lacking and thus limit the design and optimization of non-destructive testing and evaluation techniques. The laser generated ultrasound propagation in complex structures is an intricate phenomenon and is extremely hard to analyze. Only simple geometries can be studied analytically. Numerical techniques found in the literature have pr…

Electronic Transport in carbon nanotubes under traction, bending, torsion and misalignment of the two ends

Carbon Nanotube-Reinforced Nanocomposites.

A penalty-based interface technology

Modern computers have enabled engineers to perform large scale analyses of complex structures like entire aircrafts, automobiles, and ships. One issue that arises often is the need to perform a unified analysis of a structural assembly using sub-structural models created independently. These sub-structural models are frequently designed by different engineers, thus they are likely to be incompatible at their interfaces. Finite element interface technology has been developed to facilitate the joining of independently modeled substructures. Here an effective and robust interface element is presented. This method has been developed using penalty constraints and allows computationally efficient…

Effects of interfacial adhesion between phases on the stiffness of carbon nanotube reinforced nanocomposite with polymer matrix

Laser Ultrasonic Technique for Laser Powder Deposition Inspection

Numerical model for the characterization of biocomposites reinforced by sisal fibres

Abstract Although several works have been recently published in literature about biocomposites, i.e. on innovative and ecofriendly polymer matrix composites reinforced by natural fibers, there are not studies on the influence of the waviness that various natural fiber present after their extraction. In order to give a contribution to the knowledge of the effects of the fiber waviness on the main mechanical properties of biocomposites, as the longitudinal Young modulus, in the present study a systematic numerical analysis has been carried out by using parametric models properly developed, that let the user to consider the effects of the key influence parameters as the fiber concentrations an…

Mixed finite element-tight-binding electromechanical analysis of carbon nanotubes

Electrical transport properties of carbon nanotubes can be dramatically changed by mechanical deformations that alter tube shape and the corresponding positions of the atoms comprising the tube wall. In principle, detailed atomic/electronic calculations can provide both the deformed configuration and the resulting electrical transport behavior of the tube. Here we simplify the process by refining a previously-developed nonlinear structural mechanics finite-element-based procedure for modeling mechanical behavior of carbon nanotubes to account explicitly for tube chirality. A quadrilateral element overlay procedure provides an isotropic finite element model of hexagonal cells within a graphe…

Parameters influencing the stiffness of composites reinforced by carbon nanotubes – A numerical–analytical approach

Abstract Due to their high stiffness and strength, as well as their electrical conductivity, carbon nanotubes are under intense investigation as fillers in polymer matrix composites. The nature of the carbon nanotube/polymer bonding and the curvature of the carbon nanotubes may strongly reduce the reinforcing effect of the carbon nanotubes when added to a matrix to create composites. Here the effects of carbon nanotube waviness and the interaction with the matrix on the stiffness of the composite are investigated. Using a mixed numerical–analytical model, a parametric study of the waviness and volume fraction influence of CNTs on the elastic behavior of the nanocomposite is presented. The m…

Cohesive Model for the Simulation of Crack Initiation and Propagation in Mixed-Mode I/II in Composite Materials

A cohesive element able to connect and simulate crack growth between independently modeled finite element subdomains with non-matching meshes is proposed and validated. The approach is based on penalty constraints and has several advantages over conventional FE techniques in disconnecting two regions of a model during crack growth. The most important is the ability to release portion of the interface that are smaller than the local finite element length. Thus, the growth of delamination is not limited to advancing by releasing nodes of the FE model, which is a limitation common to the methods found in the literature. Furthermore, it is possible to vary the penalty parameter within the cohes…

New concept in bioderived composites: Biochar as toughening agent for improving performances and durability of agave-based epoxy biocomposites

Biocomposites are increasingly used in the industry for the replacement of synthetic materials, thanks to their good mechanical properties, being lightweight, and having low cost. Unfortunately, in several potential fields of structural application their static strength and fatigue life are not high enough. For this reason, several chemical treatments on the fibers have been proposed in literature, although still without fully satisfactory results. To overcome this drawback, in this study we present a procedure based on the addition of a carbonaceous filler to a green epoxy matrix reinforced by Agave sisalana fibers. Among all carbon-based materials, biochar was selected for its environment…

A mesh independent interface technology for simulation of mixed-mode delamination growth in laminated composites

An effective interface element technology is presented for connecting and simulating crack growth between independently modeled finite element subdomains (e.g., composite plies). This method has been developed using penalty constraints and allows coupling of finite element models whose nodes do not necessarily coincide along their common interface. Additionally, the present formulation leads to a computational approach that is very efficient and completely compatible with existing commercial software. The present interface element has been implemented in the commercial finite element code ABAQUS as a user element subroutine (UEL), making it easy to test the approach for a wide range of prob…

PROPAGAZIONE DI ONDE DI RAYLEIGH LUNGO SUPERFICI CURVE: UNO STUDIO NUMERICO E SPERIMENTALE

Il fenomeno della propagazione delle onde di superficie lungo confini rettilinei (superfici piane) è stato studiato adeguatamente. Tuttavia le indagini riguardanti la loro propagazione in superfici cilindriche sono limitate e risultano insufficienti ai fini di un loro utilizzo nelle tecniche d’ispezione non distruttive (NDE), nonostante possano essere di grande interesse per svariate applicazioni. E’ stato dimostrato sperimentalmente che l’onda superficiale subisce un cambiamento di fase durante la sua propagazione lungo una superficie cilindrica. Un approccio numerico è stato sviluppato per studiare questi effetti per diversi materiali, curvature e frequenze. I risultati numerici e sperime…

Carbon Nanotubes and Carbon Nanotube Reinforced Nanocomposites

Mechanical and Electrical Behavior of Carbon Nanotubes

Impeller optimization in crossflow hydraulic turbines

Crossflow turbines represent a valuable choice for energy recovery in aqueducts, due to their constructive simplicity and good efficiency under variable head jump conditions. Several experimental and numerical studies concerning the optimal design of crossflow hydraulic turbines have already been proposed, but all of them assume that structural safety is fully compatible with the sought after geometry. We show first, with reference to a specific study case, that the geometry of the most efficient impeller would lead shortly, using blades with a traditional circular profile made with standard material, to their mechanical failure. A methodology for fully coupled fluid dynamic and mechanical …

Simulation of laser-generated ultrasonic wave propagation in solid media and air with application to NDE

Ultrasonic methods are well known as powerful and reliable tool for defect detection. In the previous decades focus and interest have been directed to non-contact sensors and methods, showing many advantages over contact techniques where inspection depends on contact conditions (pressure, coupling medium, contact area). The non-contact hybrid ultrasonic method described here is of interest for many applications, requiring periodic inspection in service or after manufacturing. Despite the potential impact of laser-generated ultrasound in many areas of industry, robust tools for studying the phenomenon are lacking and thus limit the design and optimization of non-destructive testing and evalu…

Numerical-Analytical Model for Nanotube-Reinforced Nanocomposites

A novel numerical model able to predict the elastic properties of carbon nanotube/polymer composites containing a random distribution of CNTs has been developed. The new technique, which takes into account of the curvature that the nanotubes show when immersed in the polymer, is based on a numerical-analytical approach that has significant advances over micromechanical modeling and can be applied to several kinds of nanostructured composites. The nature of carbon nanotube/polymer bonding has arisen as key factor in the efficacy of the carbon nanotubes to actually provide any enhanced stiffness or strength to the composite. Here the effects of carbon nanotube interface interaction with the m…

Fine Alignment of Thermographic Images for Robotic Inspection of Parts with Complex Geometries

Increasing the efficiency of the quality control phase in industrial production lines through automation is a rapidly growing trend. In non-destructive testing, active thermography techniques are known for their suitability to allow rapid non-contact and full-field inspections. The robotic manipulation of the thermographic instrumentation enables the possibility of performing inspections of large components with complex geometries by collecting multiple thermographic images from optimal positions. The robotisation of the thermographic inspection is highly desirable to improve assessment speed and repeatability without compromising inspection accuracy. Although integrating a robotic setup fo…

Mixed Numerical-Analytical Model for Predicting the Elastic Properties of Nanocomposites with Random Distribution of CNTs

Simulation of the electromechanical behavior of multiwall carbon nanotubes.

The enormous potential of carbon nanotubes (CNTs) as primary components in electronic devices and NEMS necessitates the understanding and predicting of the effects of mechanical deformation on electron transport in CNTs. In principle, detailed atomic/electronic calculations can provide both the deformed configuration and the resulting electrical transport behavior of the CNT. However, the computational expense of these simulations limits the size of the CNTs that can be studied with this technique, and a direct analysis of CNTs of the dimension used in nanoelectronic devices seems prohibitive at the present. Here a computationally effective mixed finite element (FE)/tight-binding (TB) appro…

Multiwalled carbon nanotube reinforced polymer composites

Due to their high stiffness and strength, as well as their electrical conductivity, carbon nanotubes are under intense investigation as fillers in polymer matrix composites. The nature of the carbon nanotube/polymer bonding and the curvature of the carbon nanotubes within the polymer have arisen as particular factors in the efficacy of the carbon nanotubes to actually provide any enhanced stiffness or strength to the composite. Here the effects of carbon nanotube curvature and interface interaction with the matrix on the composite stiffness are investigated using micromechanical analysis. In particular, the effects of poor bonding and thus poor shear lag load transfer to the carbon nanotube…

An optimised tapered shape of the terminal contact elements in biological attachment devices

Many biological attachment devices of insects, spiders and geckoes consist of arrays of hairs (setae), which are terminated by contact elements of different shapes. However, the most frequently observed shape is a thin plate-like spatula. In spite of a rather wide range of sizes and thicknesses, most spatulae of different animals are not uniform but possess a gradient in thickness. The thickness of spatulae in the longitudinal section becomes gradually thinner close to the tip. This geometrical effect is numerically explained in the present paper, by using a numerical approach for modeling the van der Waals-like adhesion and friction between the contact element and the substrate. The approa…

Wind tunnel testing, numerical analyses and shape optimization of a vertical axis wind turbine

In this work the aerodynamic efficiency of a small commercial vertical axis wind turbine is investigated experimentally and numerically. The turbine is a Darrieus type with three vertical airfoil blades having helical twist of 78 degrees, height 1.45m and diameter of 1.45m. The airfoils have a chord of 222 mm and a thickness of 35 mm. The experimental studies were made in a wind tunnel where a hot-wire anemometer was used to measure the wind speed. The power curves of the turbine were extracted using a generator connected with an inverter able to vary the resistant moment applied to the turbine and to measure its resulting angular speed. The energy produced by the turbine itself at various …

Electromechanical behavior of carbon nanotubes under traction, bending, torsion and misalignment of the two ends

Carbon nanotubes (CNTs) can be metallic or semiconductors depending simply on geometric characteristics [e.g., 1]. This peculiar electronic behavior, combined with high mechanical strength, make them potential building blocks of a new nano-electronic technology. Most discussions of the electronic structure of CNTs assume perfect cylindrical symmetry, but this is somewhat of an oversimplification. High resolution images of CNTs often disclose structural deformations such as bent, twisted, or collapsed tubes. These deformations may develop during growth, deposition, and processing, or upon interaction with other CNTs, and with surfaces and surface features such as electrodes. Deformations bre…

Novel non-destructive inspection techniques for laser powder deposition inspection

A novel non-destructive testing (NDT) techniques for inspection of parts and components manufactured by Additive Manufacturing Processes (AMP), in particular Laser Metal Deposition (LMD), has been developed. LMD is a technology that has been maturing over the last 20 years and has found application in repair, coatings, hybrid build and 3D near net shape manufacture of small intricate parts that can be used in aero and automobile engines to improve efficiency. Currently this technology cannot be used to supply some of these parts because absence of flaws, which might be left in the component during manufacture, cannot be guaranteed. Today, quality is assessed by sample destructive testing, w…

STUDIO DELLE PROPRIETÀ MECCANICHE ED ELETTRONICHE DI NANOTUBI IN CARBONIO E DI MATERIALI COMPOSITI DERIVABILI MEDIANTE UN NUOVO APPROCCIO NUMERICO MISTO ELEMENTI FINITI – TIGHT BINDING

Rapid evaluation of notch stress intensity factors using the peak stress method with 3D tetrahedral finite element models: Comparison of commercial codes

The peak stress method (PSM) allows a rapid application of the notch stress intensity factor (NSIF) approach to the fatigue life assessment of welded structures, by employing the linear elastic peak stresses evaluated by FE analyses with coarse meshes. Because of the widespread adoption of 3D modeling of large and complex structures in the industry, the PSM has recently been boosted by including four-node and ten-node tetrahedral elements of Ansys FE software, which allows to discretize complex geometries. In this paper, a Round Robin among eleven Italian Universities has been performed to calibrate the PSM with seven different commercial FE software packages. Several 3D mode I, II and III …

Reinforcing effect of carbon nanotubes (CNT) on polymer nanocomposites – A numerical-analytical study

A mixed model, numerical-analytical, is presented that allows one to predict the elastic properties of carbon nanotube (CNT)/polymer composites containing a random distribution of CNTs, while taking account of the curvature that they show when immersed in the polymer. This hybrid approach is a significant advance over micromechanical modeling and can be applied to all nanostructured composites.

Simulation of the Stress–strain Behavior of Single and Multiwall Carbon Nanotubes-reinforced Polymer Composites

Surface waves on cylindrical solids: numerical and experimental study.

The use of Rayleigh waves enables the solution of several important inspection problems. Propagation of surface waves along straight boundaries has been properly studied but investigations about their propagation on cylindrical surfaces are not sufficient, despite they can be still of interest for NDE applications. It has been proved experimentally that a surface wave pulse suffers a phase shift during its propagation along a cylindrical surface. A numerical approach has been developed to efficiently study these effects for different materials, curvatures and frequencies. This study can help the scientific community to better understand the phenomenon, quite complex and not yet fully explor…

Effects of Mechanical Deformations on the Electrical Properties of Single and Multiwall Carbon Nanotubes

An Equivalent Orthotropic Representation of the Nonlinear Elastic Behavior of Multiwalled Carbon Nanotubes

An equivalent orthotropic representation (EOR) of the nonlinear elastic behavior of multiwalled carbon nanotubes (MWCNTs) was developed based on a nested shell structural representation of MWCNTs. The EOR model was used together with the finite element method to simulate the large deformation of MWCNTs under bending, axial compression and radial compression. Results were compared with those of the nested shell model for four-, eight-, nine-, 14-, and 19-walled carbon nanotubes. The EOR model provides a dramatic improvement in computational efficiency and successfully quantitatively replicates the overall deformation behavior including the initial linear elastic behavior, the onset of local …

Modello numerico-analitico per la caratterizzazione di nanocompositi a matrice polimerica rinforzati da nanotubi di carbonio

Numerical simulations demonstrate that the double tapering of the spatualae of lizards and insects maximize both detachment resistance and stability

Many biological attachment devices of insects, spiders and geckos consist of arrays of hairs (setae), which are terminated by contact elements of different shapes. However, the most frequently observed shape is a thin plate-like spatula. In spite of a rather wide range of sizes, most spatulae of different animals are not uniform, but rather possess a gradient in thickness and width. Here we show that the spatulae of insects and geckos become gradually thinner and wider approaching the end. This geometrical effect is explained in the present paper, by using a numerical approach for the modelling of the van der Waals adhesion and friction between the contact elements and the substrate. The ap…

Mechanical Properties of CNT/Polymer

Abstract The high mechanical properties, the stiffness-to-weight and strength-to-weight make the carbon nanotubes a perfect reinforcing agents in advanced composites. This interesting potential has attracted the attention of both industry and academia that have committed to this research field an impressive amount of work. Several applications of carbon nanotubes enriched polymer composites have already been seen: aerospace structures, sporting goods, automotive components, medical devices, optical barriers, photovoltaic devices, conducting plastics, electromagnetic interference shielding, efficient electrostatic painting of plastics, composite mirrors, plastics with high thermal dissipatio…

Calculation of the Electromechanical Properties of CNTs Under Deformation by Means of a Novel Numerical Model

The effects of mechanical deformation on the electron transport behavior of carbon nanotubes (CNTs) are of primary interest due to the enormous potential of nanotubes in making electronic devices and nanoelectromechanical systems (NEMS). Moreover it could help to evaluate the presence of defects or to assess the type of CNTs that were produced. Conventional atomistic simulations have a high computational expense that limits the size of the CNTs that can be studied with this technique. Here we present a novel numerical approach able to simulate the electromechanical behavior of SWNTs and MWNTs of the dimensions used in nano-electronic devices. The numerical model was designed to realize orde…

The Role of Patient-Specific Morphological Features of the Left Atrial Appendage on the Thromboembolic Risk Under Atrial Fibrillation

BackgroundA large majority of thrombi causing ischemic complications under atrial fibrillation (AF) originate in the left atrial appendage (LAA), an anatomical structure departing from the left atrium, characterized by a large morphological variability between individuals. This work analyses the hemodynamics simulated for different patient-specific models of LAA by means of computational fluid–structure interaction studies, modeling the effect of the changes in contractility and shape resulting from AF.MethodsThree operating conditions were analyzed: sinus rhythm, acute atrial fibrillation, and chronic atrial fibrillation. These were simulated on four patient-specific LAA morphologies, each…

Design of a wiper as compliant mechanisms with a monolithic layout

The increasingly important need to design simpler structures, reducing the number of constituent components, has motivated the approach outlined in this paper which proposes an effective re-engineering example of a product belonging to the automotive industry, combining the advantages offered by the compliant mechanisms with production opportunities linked to the use of additive manufacturing. Take advantage of compliant mechanisms makes it possible to significantly improve the component's production phase, leading to undoubted benefits on the supply chain and on product’s time to market, benefits made possible by exploiting the outstanding characteristic of additive manufacturing to produc…

Carbon Nanotube Based Composites: Processing, Properties, Modelling and Application

The object of this book is to bring together all available information on the carbon nanotube based composites. Details of the more important processing techniques for manufacturing carbon nanotubes-polymer composites are discussed in Chapter 1, including preprocessing treatments as purifi-cation, graphitization and functionalization. Chapters 2 explores the state of the art concern-ing mechanical, thermal, electrical and optical properties of CNTs composites made of the most frequently used polymer matrixes. Two tables gives quick access to a vast amount of the available data on the mechanical and electrical properties of CNTs composites. In Chapter 3 a reviews of the numerical models, whi…

HIGH-EFFICIENCY OSCILLATING-BLADE WIND TURBINE

A Mesh Independent Penalty Based Finite Element Solution for Mixed-Mode Delamination Propagation in Composites

Micromechanical modeling of carbon nanotube-reinforced nanocomposites

A computational approach to direct simulation of realistic sized single and multiwall carbon nanotubes

TURBINA EOLICA A PALE OSCILLANTI AD ELEVATO RENDIMENTO

Il presente brevetto ha per oggetto una turbina eolica ad asse verticale caratterizzata da pale che oscillando consentono di massimizzare il rendimento nella trasformazione dell’energia eolica in energia meccanica, successivamente trasformabile in energia elettrica. Grazie al particolare disegno costruttivo le pale si orientano automaticamente in modo da opporre al vento la massima superficie possibile delle pale che si muovono nella direzione del vento minimizzando al tempo stesso la superficie delle pale che si muovono controvento. La presenza di una elevata superficie esposta all’azione del vento, non contrastata da una azione frenante dovuta alle pale controvento, consente di ottenere s…

MODELLO NUMERICO PER LA CARATTERIZZAZIONE DI MATERIALI COMPOSITI A MATRICE POLIMERICA RINFORZATI DA NANOTUBI DI CARBONIO

Numerical model for composite material with polymer matrix reinforced by carbon nanotubes

Due to the high stiffness and strength, as well as their ability to act as conductors, carbon nanotubes are under intense investigation as fillers in polymeric materials. The nature of the carbon nanotube/polymer bonding and the curvature of the carbon nanotubes within the polymer have arisen as particular factors in the efficacy of the carbon nanotubes to actually provide any enhanced stiffness or strength to the nanocomposite. Here the effects of carbon nanotube curvature and interface interaction with the matrix on the nanocomposite stiffness are investigated using nanomechanical analysis. In particular, the effects of poor bonding and thus poor shear lag load transfer to the carbon nano…

Ruolo della variazione di larghezza e di spessore nelle spatole delle lucertole e degli insetti

Molti dispositivi biologici di adesione degli insetti, dei ragni e dei gechi consistono di matrici di peli (setae) che terminano con elementi di contatto di diverse forme. Tuttavia, la forma più osservata è una spatola appiattita. Nonostante nei diversi animali le spatole esistano in una notevole varietà di dimensioni, la maggior parte di esse non sono uniformi ma posseggono un gradiente sia in spessore che in larghezza. In questo lavoro investighiamo perché le spatole dei gechi diventano gradualmente più sottili e più larghe avvicinandosi alla loro estremità. Il motivo di questa particolare geometria è studiato utilizzando un approccio numerico basato sul metodo degli elementi finiti. La m…

Design of a telescopic tower for wind energy production with reduced environmental impact

A prototype of a telescopic pole for wind energy production with low environmental impact and its lifting system for a 60 to 250 kW turbine and a height of 30 m have been designed and manufactured. A telescopic tower, which is raised and lowered by automation or by remote control, allows to differentiate the presence of the generator within the landscape over time. The technology currently available for lifting and lowering wind turbines is made up of telescopic poles of heights of less than 10 meters and with tilting posts of height below 30 m. Without a state of the art to refer to, the telescopic pole and its lifting system have been designed starting from scratch and solving with innova…

ELECTROMECHANICAL PROPERTIES OF SINGLE AND MULTIWALL CARBON NANOTUBES UNDER MECHANICAL DEFORMATION

Rapid evaluation of notch stress intensity factors using the peak stress method: Comparison of commercial finite element codes for a range of mesh patterns

The peak stress method (PSM) is an engineering, finite element (FE)-oriented method to rapidly estimate the notch stress intensity factors by using the singular linear elastic peak stresses calculated from coarse FE analyses. The average element size adopted to generate the mesh pattern can be chosen arbitrarily within a given range. Originally, the PSM has been calibrated under pure mode I and pure mode II loadings by means of Ansys FE software. In the present contribution, a round robin between 10 Italian universities has been carried out to calibrate the PSM with 7 different commercial FE codes. To this aim, several two-dimensional mode I and mode II problems have been analysed independe…

A numerical-analytical model for the characterization of composites reinforced by carbon nanotubes

A mixed model, numerical-analytical, is presented that allows one to predict the elastic properties of carbon nanotube (CNT)/polymer composites containing a random distribution of CNTs, while taking account of the curvature that they show when immersed in the polymer. This hybrid approach is a significant advance over micromechanical modeling and can be applied to all nanostructured composites.

A mixed finite element-tight binding technique for studying the electromechanical behavior of single and multiwall carbon nanotubes

Mechanical properties of carbon nanotube fibres: St Venant’s principle at the limit and the role of imperfections

Abstract Carbon nanotube (CNT) fibres, especially if perfect in terms of their purity and alignment, are extremely anisotropic. With their high axial strength but ready slippage between the CNTs, there is utmost difficulty in transferring uniformly any applied force. Finite element analysis is used to predict the stress distribution in CNT fibres loaded by grips attached to their surface, along with the resulting tensile stress–strain curves. This study demonstrates that, in accordance with St Venant’s principle, very considerable length-to-diameter ratios (∼103) are required before the stress becomes uniform across the fibre, even at low strains. It is proposed that lack of perfect orienta…

Studio numerico e sperimentale sulla generazione degli ultrasuoni tramite sorgente laser puntiforme

An experimental and numerical study on the ultrasonic fields generated in metals by a point laser source has been done. Energy and profile of the beam, pulse duration, extent and shape of the irradiated area affect amplitude, frequency and directionality of the ultrasonic waves. The study has been developed for the thermoelastic regime, where the laser radiation with low energy density limits the amplitude of ultrasounds and therefore the sensitivity in detecting the defects in extended bodies. By controlling some parameters the signal-to-noise ratio can be increased. The experimental study has been conducted by varying the impact area, the distribution of the beam energy in the impact area…

Electrical Conduction in Carbon Nanotubes under Mechanical Deformations

The enormous potential of carbon nanotubes (CNTs) as primary components in electronic devices and NEMS necessitates the understanding and predicting of the effects of mechanical deformation on electron transport in CNTs. In principle, detailed atomic/electronic calculations can provide both the deformed configuration and the resulting electrical transport behavior of the CNT. However, the computational expense of these simulations limits the size of the CNTs that can be studied with this technique and a direct analysis of CNTs of the dimension used in nano-electronic devices, particularly multi-wall CNTs (MWNTs), seems prohibitive at the present. Here a computationally effective mixed finit…

An Improved Thermal Lamination Model for Analysis of Heat Transfer in Composite Structures

A new thermal lamination model and its associated finite element model are presented for analysis of heat transfer in laminated composite structures. The form of the present model closely resembles that of recent zig-zag sublaminate structural laminate theories. The through-thickness distribution of temperature is assumed to vary linearly within each ply, and continuity of transverse flux at ply interfaces is enforced analytically. Thus, the number of computational degrees-offreedom (DOFs) is made independent of the number of plies in the sublaminate. In its present form, the model contains only two computational DOFs in each sublaminate–the temperature at the top and bottom surface of the…

Mechanics of Axial Compression of Single and Multi Wall Carbon Nanotubes

Mechanics of deformation of single- and multi-wall carbon nanotubes

Abstract An effective continuum/finite element (FE) approach for modeling the structure and the deformation of single- and multi-wall carbon nanotubes (CNTs) is presented. Individual tubes are modeled using shell elements, where a specific pairing of elastic properties and mechanical thickness of the tube wall is identified to enable successful modeling with shell theory. The incorporation and role of an initial internal distributed stress through the thickness of the wall, due to the cylindrical nature of the tube, are discussed. The effects of van der Waals forces, crucial in multi-wall nanotubes and in tube/tube or tube/substrate interactions, are simulated by the construction of special…

UN MODELLO NUMERICO PER LA INTERPRETAZIONE DEL COMPORTAMENTO MECCANICO DI BIOCOMPOSITI RINFORZATI CON FIBRE DI AGAVE

Sebbene diversi lavori siano stati pubblicati recentemente in letteratura sui biocompositi, ovvero su innovativi materiali compositi a matrice polimerica rinforzati con fibre naturali, nessuno studio è stato sino ad ora condotto sugli effetti legati alla naturale forma ondulata assunta da diverse fibre naturali, come per esempio l’agave sisalana, a seguito della estrazione. Nel caso, piuttosto ricorrente nella sperimentazione, di laminazione di biocompositi a fibre lunghe senza uso di apposti tessuti unidirezionali confezionati previo accurato stiramento e allineamento delle fibre, si ottengono laminati le cui proprietà meccaniche possono essere in linea di principio influenzate significati…

Studio delle proprietà meccaniche di compositi rinforzati con nanotubi in carbonio mediante un nuovo approccio numerico misto

I CNTs primeggiano in rigidezza, resistenza a rottura, resilienza, allungamento a rottura, conducibilità termica e conducibilità elettrica. Un modo di avvantaggiarsi delle loro singolari proprietà consiste nell’incorporarli in una matrice per costruire materiali compositi nanostrutturati. Questo articolo presenta un nuovo modello misto, numerico-analitico, che consente di prevedere le caratteristiche elastiche di nanocompositi con distribuzione random dei CNTs, tenendo conto della curvatura che gli stessi mostrano quando sono immersi nel polimero. L’approccio ibrido rappresenta un’apprezzabile evoluzione della modellazione micromeccanica e può essere applicato a qualsiasi composito nanostru…

Materiali Compositi Rinforzati da Nanotubi di Carbonio a Parete Multipla

Experimental and numerical method for nondestructive ultrasonic defect detection

Ultrasonic methods are well known as powerful and reliable tool for defect detection. Conventional ultrasonic techniques rely generally on piezoelectric transducers where transmission of energy to the material is achieved with contact. In the last decades focus and interest have been directed to non-contact sensors and methods, showing many advantages over contact techniques where inspection depends on contact conditions (pressure, coupling medium, contact area). The growing interest is also due to the further development of air-coupled probes, thanks to new materials for acoustic devices and manufacturing technologies. The use of laser as tool for ultrasonic defect detection is also an eme…

Numerical study for a new methodology of flaws detection in train axles

Train loads and travel speeds have increased over time, requiring more efficient non-destructive inspection methods. Railway axles are critical elements; despite being designed to last more than 20 years several cases of premature failure have been recorded. Train axles are inspected regularly, but the limits associated to the traditional inspection technologies create a growing interest towards new solutions. Here a novel non-destructive inspection method of in-service axles based on non-contact data collection is presented. The propagation of surface waves, generated by a thermo-elastic laser source, is investigated using a finite element method based on dynamic explicit integration. Coup…

3D simulations and experiments of guided wave propagation in adhesively bonded multi-layered structures

Understanding guided wave propagation in multi-layered plates and interaction with discontinuities can be difficult, as well as the interpretation of the ultrasonic signals. Propagation of guided waves can be studied analytically solving the equations of motion with the proper boundary conditions; nevertheless analytical models can be difficult to solve for complex multi-layered structures or having inner discontinuities. The problem can be efficiently studied using numerical techniques. Simulation of guided wave propagation in multi-layered structures, for ultrasonic waves in the MHz range, is solved here with the finite element analysis based on an explicit integration rule to solve the e…

Novel non-destructive evaluation technique for the detection of poor dispersion of carbon nanotubes in nanocomposites

Abstract A wide use of advanced carbon nanotube polymer composites can be boosted by new non-destructive evaluation (NDE) techniques that can test the quality of the products to ensure that their specifications are met. It is well known in literature that the parameter that far more than others can affect the enhancing capabilities of the carbon nanotubes is their dispersion. Here we have presented a novel NDE technique based on infrared thermography able to evaluate the dispersion of the added nanoparticles in polymer nanocomposites. The NDE technique was used to compare pairs of samples whose difference is represented only by the level of dispersion. It was found a significant difference …

Electromechanical Behavior of Single and Multiwall Carbon Nanotubes

Carbon nanotubes (CNTs) can be metallic or semiconductors depending simply on geometric characteristics. This peculiar electronic behavior, combined with high mechanical strength, make them potential building blocks of a new nano-electronic technology. High resolution images of CNTs often disclose structural deformations such as bent, twisted, or collapsed tubes. These deformations break the tube symmetry, and a change in their electronic properties should result. A computationally effective mixed finite element-tight-binding approach able to simulate the electromechanical behavior of single and multiwall nanotubes used in nano-electronic devices is presented. The finite element (FE) comput…

Electronic and Transport Properties of Single and Multiwall Carbon Nanotubes under Mechanical Deformations

A New Thermal Theory for Thermo-Mechanical Analysis of Composites

The use of laminated and sandwich construction to achieve multi-functional objectives within a single structure continues to increase. It is especially desirable to use laminated construction in structures exposed to thermal loading, where heat resistant coating materials may be bonded to traditional structural materials. Design of such structures requires an accurate analysis of stresses induced by thermal as well as mechanical loads. A novel laminated plate theory and 3D finite element model based on first-order zig-zag sublaminate approximations are presented for thermal stress analysis of composite laminates and sandwich plates. The finite element is developed with the topology of an ei…

Analysis of the Parameters Affecting the Stiffness of Short Sisal Fiber Biocomposites Manufactured by Compression-Molding

The use of natural fiber-based composites is on the rise in many industries. Thanks to their eco-sustainability, these innovative materials make it possible to adapt the production of components, systems and machines to the increasingly stringent regulations on environmental protection, while at the same time reducing production costs, weight and operating costs. Optimizing the mechanical properties of biocomposites is an important goal of applied research. In this work, using a new numerical approach, the effects of the volume fraction, average length, distribution of orientation and curvature of fibers on the Young’s modulus of a biocomposite reinforced with short natural fibers were stud…

Finite-Element Interface Technology for Modeling Delamination Growth in Composite Structures

OTTIMIZZAZIONE FLUIDO-MECCANICA DI TURBINE IDRAULICHE CROSSFLOW

Electrical conductance in carbon nanotubes under mechanical deformation

Enhancement of Static and Fatigue Strength of Short Sisal Fiber Biocomposites by Low Fraction Nanotubes

AbstractThanks to good mechanical performances, high availability, low cost and low weight, the agave sisalana fiber allows to obtain biocomposites characterised by high specific properties, potentially very attractive for the replacement of synthetic materials in various industrial fields. Unfortunately, due to the low strength versus transversal damage processes mainly related to the matrix brittleness and/or to the low fiber/matrix adhesion, the tensile performance of random short fiber biocomposites are quite low, and to date most of the fiber treatments proposed in literature to improve the fiber-matrix adhesion, have not led to very satisfactory results. In order to overcome such a dr…

Numerical model for the electromechanical characterization of carbon nanotubes

Carbon nanotubes (CNTs) can be metallic or semiconductors depending simply on geometric characteristics [e.g., 1]. This peculiar electronic behavior, combined with high mechanical strength, make them potential building blocks of a new nano-electronic technology. Most discussions of the electronic structure of CNTs assume perfect cylindrical symmetry, but this is somewhat of an oversimplification. High resolution images of CNTs often disclose structural deformations such as bent, twisted, or collapsed tubes. These deformations may develop during growth, deposition, and processing, or upon interaction with other CNTs, and with surfaces and surface features such as electrodes. Deformations bre…

PROPAGAZIONE DI ONDE GUIDATE IN LAMINATI MULTISTRATO INCOLLATI: ANALISI NUMERICA E SPERIMENTALE

A penalty-based finite element interface technology

Abstract An effective and robust interface element technology able to connect independently modeled finite element subdomains is presented. This method has been developed using the penalty constraints and allows coupling of finite element models whose nodes do not coincide along their common interface. Additionally, the present formulation leads to a computational approach that is very efficient and completely compatible with existing commercial software. A significant effort has been directed toward identifying those model characteristics (element geometric properties, material properties and loads) that most strongly affect the required penalty parameter, and subsequently to developing si…

Hybrid nanocomposites with ultra-low filling content by nano-coating fragmentation

In the current study, a new technique for the manufacturing of polymer nanocomposites (PNCs) with ultra-low filling content (<0.05 wt%) is presented. Specifically, this method has been validated through the production of polypropylene (PP) nanocomposites with Ag nanoparticles. The presented method first consisted in a metal nano-film deposition on PP pellet substrates by a physical vapor deposition (PVD) sputtering equipment. Subsequently, a percentage of the coated pellet was mixed to uncoated ones via an injection molding machine to produce the PNC in a single step. Different mixing percentages of coated PP pellet to the uncoated ones were studied. As a result, the fragmentation of the…

Effects of mechanical deformation on electronic transport through multiwall carbon nanotubes

Abstract The effects of mechanical deformation on the electron transport behavior of carbon nanotubes (CNTs) are of primary interest due to the enormous potential of nanotubes in making electronic devices and nanoelectromechanical systems (NEMS). Moreover it could help to evaluate the presence of defects or to assess the type of CNTs that were produced. Conventional atomistic simulations have a high computational expense that limits the size of the CNTs that can be studied with this technique and a direct analysis of CNTs of the dimension used in nano-electronic devices seems prohibitive at the present. Here a novel approach was designed to realize orders-of-magnitude savings in computation…

Modello numerico per la caratterizzazione elettromeccanica dei nanotubi di carbonio

Nell’ultimo decennio i nanotubi di carbonio (Carbon nanotubes, CNTs) hanno suscitato un considerevole interesse nella comunità scientifica internazionale a causa delle loro proprietà meccaniche, bassa densità ed elevata conducibilità termica. I CNT possiedono inoltre peculiari proprietà elettroniche dipendenti da elicoicità e stato di deformazione, rendendoli potenziali elementi costruttivi di una nuova tecnologia nano-elettronica. Numerosissimi dispositivi elettronici basati sui CNTs (transistors, nano-switches, attuatori, ecc.) sono già stati realizzati. Un nuovo approccio è stato sviluppato per investigare la deformazione dei CNTs e si basa su modelli agli elementi finiti accuratamente s…

Mechanical properties of carbon nanotube reinforced nanocomposites

One way to take advantage of the marvelous properties of the carbon nanotubes consists in incorporating them into a matrix to build composite materials. The best candidates for this task are undoubtedly polymers thanks to their strength, toughness, low weight, and easy processing. A mixed model, numerical-analytical, is presented that allows one to predict the elastic properties of carbon nanotube (CNT)/polymer composites containing a random distribution of CNTs, while taking account of the curvature that they show when immersed in the polymer. A three-dimensional model, using a single CNT immersed in an infinite matrix, allows us to numerically evaluate the concentration tensor by evaluati…