1,721,038 research outputs found
Nanoscale Non-destructive Testing with the Atomic Force Microscope
No full textThrough implementing ultrasound detection with the AFM, a new branch of subsurface non-destructive testing has emerged which allows for nanoscale defect characterization. A systematic study was carried out with AFAM to determine its subsurface detection limitations on a stiff material. AFAM was able to reliably detect 2.5 μm diameter holes through a maximum graphite thickness of 570 nm and sub 100 nm holes through 140 nm of graphite. Various operating parameters such as contact force and cantilever eigenmode were found to increase contrast of the subsurface holes, however the smallest detectable defect remained the same. In an attempt to push the detection sensitivity, a humidity study was performed with AFAM where the presence of water showed negligible effects on subsurface contrast. HFM was implemented and showed comparable sensitivity to AFAM on detecting nanosized defects through graphite. Lastly, AFAM showed proficiency in detecting delamination at the interface of a graphite-polymer nanocomposite.M.A.S
Mechanical Properties of Graphene Oxide Infiltrated Carbon Nanotube Fibers
Get PDFIn this study, graphene oxide (GO) was infiltrated into the CNT fibers (i.e. voids infiltrated into the CNT fibers (i.e. voids infiltrated into the CNT fibers (i.e. voids within CNT bundles ~ 50 nm in diameter) to interlock and improve the interfacial shear strength of the fibers. GO was was selected instead of polymers due to its higher mechanical properties, similar carbon-based structures as the CNT fibers, and high temperature stability. GO particles with a diameter of approximately 50 nm, which match closely to the void size within fibers, have been found to be optimal for enhancing the mechanical properties of fibers. Tensile testing demonstrated that the optimized GO infiltrated CNT fibers exhibit improvement in stiffness, yield strength, ultimate tensile strength, and energy to failure of pristine CNT fibers of ~100%, ~110%, ~56%, and 30%, respectively.M.A.S
Mechanical Stability of Thin Films for Solid-state Batteries
Get PDFThe electrochemical performance of all-solid-state batteries (ASSBs) is limited to the mechanical instability of components. Volume expansion of components and Li dendrite formation are the main reasons for components fracture and reduced battery life. The mechanical behaviour of thin films fabricated by atomic and molecular layer deposition techniques (ALD and MLD, respectively) was studied using atomic force microscopy (AFM) based mechanical testing methods. Mechanical properties, including elastic modulus, failure forces, toughness, and fatigue, were evaluated for ALD and MLD thin films (Ph.D.2022-06-29 00:00:0
Material inspection using new electromagnetic testing technology : coplanar capacitive sensing technique
No full textLes matériaux diélectriques jouent un rôle important dans les applications industrielles et les domaines de la recherche scientifique et leur utilisation a augmenté ces dernières années. Leurs applications concernent l'industrie moderne des circuits intégrés et les réseaux d'antennes compacts. De plus, les composites structuraux légers dans l'industrie aérospatiale, les armures corporelles en Kevlar et les composites à matrice céramique pour la stabilité thermique dans les environnements chauds des moteurs sont des exemples de certaines des applications récemment développées des matériaux diélectriques. Par conséquent, la détection des défauts de ces matériaux diélectriques devient très importante pour le contrôle du processus de fabrication, l'optimisation de la conception et des performances des appareils électriques, et la surveillance et le diagnostic du système. Par conséquent, le besoin de tests de contrôle non destructifs (CND) précis des matériaux structurels et fonctionnels diélectriques a également augmenté. Cependant, le CND de ces matériaux n'est pas aussi développé que celui des métaux et de nouvelles approches pour évaluer la qualité de ces matériaux lors de la fabrication et de la maintenance n'ont pas encore été développées. Par conséquent, il sera utile de développer de nouvelles méthodes telles que des techniques de détection capacitive qui peuvent surmonter certaines des restrictions associées à d'autres techniques d'évaluation des matériaux diélectriques. La simulation numérique utilisant la modélisation par éléments finis (FEM) tridimensionnelle (3D) est utilisée dans le logiciel COMSOL Multiphysics pour simuler la distribution du champ électrique à partir d'un capteur capacitif coplanaire et la façon dont il interagit avec divers échantillons composés de différents types de défauts. Une analyse détaillée FEM est fournie pour étudier les paramètres de conception, y compris la forme/taille/distance des électrodes coplanaires pour évaluer et identifier les caractéristiques importantes des électrodes capacitives coplanaires, telles que la pénétration et la force du champ électrique en fonction du capteur propriétés géométriques. De plus, l'influence des différentes fréquences, du décollement et de la présence ou de l'absence d'une plaque de blindage métallique et d'une électrode de garde sur le résultat de sortie est analysée par la même méthode. En outre, la distribution du champ électrique, en fonction du nombre d'électrodes, à partir d'un capteur capacitif coplanaire multi-électrodes avec différents agencements d'électrodes d'entraînement et de détection, et comment ce champ peut être modifié en changeant l'agencement est simulé et illustré par le MEF 3D. Des expériences physiques sont réalisées avec plusieurs capteurs capacitifs coplanaires pour vérifier les résultats de la simulation et évaluer les performances de la sonde. Dans ces expériences, les performances d'imagerie du capteur, l'effet des paramètres de conception sur les performances du capteur, l'impact des divers matériaux testés et la faisabilité de la sonde capacitive coplanaire multi-électrodes seront pris en compte. La comparaison des résultats de simulation numérique et d'expériences physiques montre qu'ils sont en bon accord qualitatif.Dielectric materials have an extensive role in both industrial applications and scientific research areas and their use has increased in recent years. Furthermore, lightweight structural composites in the aerospace industry, Kevlar body-armour and ceramic-matrix composites for thermal stability in hot engine environments are examples of some of the recently developed applications of dielectric materials. Therefore, the flaw detection of these dielectric materials becomes markedly important for the process control in manufacturing, optimization of electrical apparatus design and performance, and system monitoring and diagnostics. Consequently, the need for accurate non-destructive testing (NDT) of dielectric structural and functional materials has also been increased. However, the NDT of such materials is not as well developed as those for metals and new approaches to evaluate the quality of these materials during manufacturing and maintenance have not yet been expanded. Therefore, it will be valuable to develop new methods such as capacitive sensing techniques which can overcome some of the restrictions associated with other techniques for assessing dielectric materials. The numerical simulation using three dimensional (3 D) Finite Element Modelling (FEM) is employed in COMSOL Multiphysics software to simulate the electric field distribution from a coplanar capacitive sensor and the way it interacts with various specimens composed of different types of defects. A detailed analysis FEM is provided to study the design parameters including the shape/size/distance of the coplanar electrodes to assess and identify the important features of the coplanar capacitive electrodes, such as the penetration and strength of the electric field as a function of sensor geometrical properties. In addition, the influence of the different frequencies, lift-off, and the presence or absence of a metal shielding plate and guard electrode on the output result is analyzed by the same method. Besides, the electric field distribution, as a function of the number of electrodes, from a multi-electrode coplanar capacitive sensor with different arrangements of driving and sensing electrodes, and how this field may be altered by changing the arrangement is simulated and illustrated by the 3D FEM. Physical experiments are carried out by several coplanar capacitive sensors to verify the simulation results and evaluate the performance of the probe. In these experiments, the imaging performance of the sensor, the effect of design parameters on the sensor performance, the impact of various materials under test, and the feasibility of the multi-electrode coplanar capacitive probe will be considered. Comparison of the numerical simulation results and physical experiments illustrate that they are in good qualitative agreement
Nanometer-scale studies of friction, dissipation, and plasticity
Get PDFMaterials exhibit dramatically different mechanical properties when probed and confined on nanometer length scales. These size effects can arise from both the nature of individual contacts and the reduced dimensions of the interacting bodies. In this thesis, multimode atomic force microscopy techniques have been applied to study mechanical size effects of friction and plasticity in bulk and ultrathin film crystalline materials. Incipient plasticity of crystal surfaces has been studied by a novel atomic force microscopy based indentation method. High resolution imaging after indentation of Cu(100) and KBr(100) surfaces revealed the resulting dislocation structure. The distribution of discontinuities observed in indentation force curves correlated to the creation of individual dislocation loops. The shear stress acting at the point of first yield was consistent with density functional theory predictions for the ideal shear strength of the crystal. Friction and dissipation in epitaxial ultrathin films was then studied by the combined techniques of non-contact force microscopy, Kelvin probe force microscopy, and friction force microscopy. Films as thin as one and two atomic layers exhibit atomic stick-slip friction loops similar to their bulk forms. Edge sites of KBr films grown on Cu(100) are prone to wear while substrate steps overgrown by the film are stable. This phenomenon can be understood in terms of enhanced interaction at low-coordinated sites as reveled by atomic-resolution imaging. The tribological benefits of a closed KBr ultrathin layer are found to be consistent with macroscopic experiments. Single layer graphene films grown on SiC(0001) exhibit a reduced local work function compared to bilayers, allowing an unambiguous identification of layer thickness. Friction on SiC is greatly reduced by a single layer of graphene, and reduced by another factor of two on bilayer graphene. The friction contrast between single and bilayer graphene arises from a diffLorsque confinés et sondés à l’échelle nanométrique, les matériaux ont des propriétés mécaniques grandement différentes. Ces effets de taille proviennent de la nature des contacts individuels et des dimensions réduites des corps en interaction. Dans cette thèse, des méthodes de microscopie à force atomique multimode ont été employées pour étudier les effets de taille mécaniques de la friction et de la plasticité dans le volume et en couches ultraminces de matériaux cristallins. L’apparition de la plasticité en surfaces cristallines a été étudiée par une méthode d’indentation novatrice basée sur la microscopie à force atomique. Des images à haute résolution après indentation de Cu(100) et KBr(100) ont révélé la structure de dislocation résultante. La distribution des discontinuités observées dans les courbes de force d’indentation sont corrélées avec la création de boucles de dislocation individuelles. Les contraintes de cisaillement agissant à la limite d’élasticité sont en accord avec les prédictions des théories à fonctionnelle de densité pour le cisaillement idéal de cristaux.La friction et la dissipation des couches ultraminces ont alors été étudiées par des techniques combinées de microscopie à force atomique hors-contact, à sonde Kelvin, et à friction. Des couches mono et biatomiques montrent des boucles de friction de glissement saccadé (stick-slip) atomique similaires aux formes de volume. Les sites en bordure de couche de KBr sur Cu(100) sont sensibles à l’usure tandis que les marches de substrat exhaussées par la couche mince sont stables. Ce phénomène se comprend comme une interaction accentuée aux sites à basse coordination, comme révélé par imagerie à résolution atomique. Les avantages tribologiques d’une couche ultra-mince fermée de KBr sont consistants avec les expériences macroscopiques. Les monocouches de graphène sur SiC(0001) montrent une fonction de travail
Tribological Properties of Ultrathin Films for MEMS Applications
No full textThe friction and wear properties of ultrathin films of graphene, graphene oxide (GO) and reduced GO at nanoscale were investigated using friction force microscopy (FFM). Graphene and GO were found to reduce friction for sliding between a Si AFM tip and SiOM.A.S
Tribological Properties of Ultrathin Films for MEMS Applications
Get PDFThe friction and wear properties of ultrathin films of graphene, graphene oxide (GO) and reduced GO at nanoscale were investigated using friction force microscopy (FFM). Graphene and GO were found to reduce friction for sliding between a Si AFM tip and SiOM.A.S
Nanomechanics and Tribology of Molybdenum-Disulphide Based Solid Lubricants for Space Applications
Get PDFMolybdenum-disulphide solid lubricant coatings have an established history of use in space applications. However, limited understanding of their breakdown and failure mechanics has led to premature failure of several systems and missions. In the present study, high-resolution nanomechanical testing techniques are used to examine specific failure mechanics of both pure and co-deposited MoS2 coatings. Fundamental properties such as fracture and shear strength are determined in relation to the nanostructural characteristics of the coatings. It is found that purely nanocrystalline MoS2 shows impeded shearing within the structure compared to partially amorphous MoS2 which therefore increases the friction and wear rates. Furthermore, three state-of-the-art co-deposited coatings are tested under earth to low-earth-orbit specific environments. The newly developed prototype coating is found to outperform the best commercially available coatings under true application-specific conditions. This increased fundamental and application-specific understanding of MoS2 based coatings allows for precision tailoring of MoS2 coatings for reliable performance.M.A.S
Nanomechanics and Tribology of Molybdenum-Disulphide Based Solid Lubricants for Space Applications
No full textMolybdenum-disulphide solid lubricant coatings have an established history of use in space applications. However, limited understanding of their breakdown and failure mechanics has led to premature failure of several systems and missions. In the present study, high-resolution nanomechanical testing techniques are used to examine specific failure mechanics of both pure and co-deposited MoS2 coatings. Fundamental properties such as fracture and shear strength are determined in relation to the nanostructural characteristics of the coatings. It is found that purely nanocrystalline MoS2 shows impeded shearing within the structure compared to partially amorphous MoS2 which therefore increases the friction and wear rates. Furthermore, three state-of-the-art co-deposited coatings are tested under earth to low-earth-orbit specific environments. The newly developed prototype coating is found to outperform the best commercially available coatings under true application-specific conditions. This increased fundamental and application-specific understanding of MoS2 based coatings allows for precision tailoring of MoS2 coatings for reliable performance.M.A.S
Mechanical Properties of Uncoated and Core-shell Silicon Nanowire Arrays for the Application of Lithium Ion Batteries
Get PDFThree types of silicon nanowires arrays: 1) Uncoated silicon nanowires; 2) Alumina-coated silicon nanowires and 3) Polymer-coated silicon nanowires have been studied with a newly developed Atomic Force Microscopy (AFM) based mechanical testing protocol regarding three mechanical properties, including: i) stress-strain slope (or slope of stress-strain curve); ii) energy dissipation and iii) strain-to-failure.
It is found that the alumina-coated silicon nanowires possessed the highest stress-strain slope, energy dissipation and strain-to-failure. The high stress-strain slope was attributed to the dominating elastic properties of the alumina coating, whereas the high energy dissipation and strain-to-failure were very likely to be due to the shearing of the alumina-silicon interface and the high friction coefficient of the alumina coating. It is concluded that short alumina-coated SiNW was the most suitable material to be used as LIB anode among the three materials tested since it can potentially tackle the mechanical issues during charging and discharging cycles.M.A.S
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