In product development there is still potential to decrease lead times with faster and more accurate simulations. The objective of this thesis was to study whether Finite Element (FE) simulations using explicit LS-DYNA to extract reaction forces from sheet metal forming tools during forming, could be used to improve existing FE models in sheet metal forming software AutoForm.To begin with, the solid CAD-model of the stamping dies were meshed with tetrahedral elements in CATIA and imported into LS-DYNA. In combination with sheet mesh and milling surface meshes from AutoForm, an explicit model was realized. Contacts between sheet mesh and milling surface meshes used the so-called sheet forming contact. The resulting reaction forces were extracted and used in a simulation using the AutoForm software. Resulting simulation was compared to a scan of the physical sheet metal after forming.The direct transfer of reaction forces from LS-DYNA to AutoForm did however not result in the same pressure distribution in AutoForm. The AutoForm simulations using results from LS-DYNA were slightly worse than standard AutoForm simulations.Further work is needed to try and perhaps implement an implicit solution after an initial explicit solution. / Inom produktutveckling finns möjligheter att förkorta ledtider genom snabbare och mera korrekta simuleringar. Syftet med detta arbetet var att undersöka huruvida resultat från explicit LS-DYNA kunde användas för att förbättra nuvarande plåtformningssimuleringar i AutoForm.Den solida CAD-modellen av verktyget meshades med tetraediska element i CATIA och importerades till LS-PrePost, tillsammans med fräsytsmeshar och plåtmesh från AutoForm. Kontakter etablerades mellan plåt och fräsytsmeshar med så kallad sheet forming contact. Modellen löstes sedan explicit. Resulterande reaktionskrafter på plåthållare exporterades till AutoForm och implementerades där. Resulterande simulering jämfördes mot en inskannad fysisk plåt efter plåtformning.Direkt implementering av reaktionskrafter på plåthållaren i AutoForm gav resultat som avvek mer mot inskannad plåt än nuvarande simuleringsstrategi. Direkt implementering av reaktionskrafter gav heller inte en tryckfördelning som liknade den som rapporterades av LS-DYNA.Mer arbete krävs för att om möjligt implementera en implicit lösning efter en initial explicit lösning.

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Damage in composite material fabricated aerospace, aeronautical, mechanical, civil and offshore structures often results from factors such as fatigue, corrosion and accidents. Such damage when left unattended can grow at an alarming rate due to the singularity of the stress and strain in the vicinity of the damage. It can lead to increase in the vibration level, reduction in the load carrying capacity, deterioration in the normal performance of the component and even catastrophic failure. In most conditions, the service life of damaged components is extended with repair instead of immediate replacement. Effective repair of structural damage is therefore an important and practical topic. Repair can extend the service life and can be a cost efficient alternative to immediate replacement of the damaged component. Most conventional repair methods involve welding, riveting or mounting additional patches on the parent structure without removing the damaged portion. These methods tend to be passive and inflexible, faced with the limitations of adjusting the repair to the changes in external loads.Besides, in certain cases these methods may lead to additional damage to the structure. For example, the in-situ drilling required in some cases can cause damage to items such as hidden or exposed hydraulic lines and electrical cables. Welding or bonding patches can cause significant stress alterations and serious stress corrosion problems, apart from burdening the weight sensitive structures. Above all, effective repair applying conventional analytical methods hinges on calculation of the singularity of stress and strain in the vicinity of the damage, which is be a difficult as only approximate solutions are available. Thus, a need is felt to update the repair methods with the advancement in fields of materials, sensing and actuating. This can make the repair more effective and efficient than conventional repair methodology. Current research proposes the use of piezoelectric materials in repair of delaminated composite structures. A detailed mechanics analysis of the delaminated beams, subjected to concentrated static loads and axial compressive loads, is presented. The discontinuity of shear stresses induced at delamination tips due to bending of the beams, under action of concentrated static load and axially compressive load, is studied. This discontinuity of the shear stresses normally leads to the sliding mode of fracture of the beam structures. In order to ensure proper functioning of these beam structures, electromechanical characteristics of piezoelectric materials are employed for their repair. Numerical simulations are conducted to calculate the repair voltage to be applied to the piezoelectric patches to erase the discontinuity of horizontal shear stress at the delamination tips and thus, render the beam repaired. The variation of repair voltage with location and size of the delamination is considered. FE simulations are performed to validate the numerically calculated voltage values. The research presented serves to provide information on the design of piezoelectric materials for the repair of delaminated composite structures.

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No description available.

Nanoelectromechanical systems (NEMS) play an important role in advancing high-precision sensing and high-speed computational applications due to their exceptional sensitivity and reduced size. This thesis explores the dynamic behaviors and vibrational properties of NEMS, focusing on coupled systems of molybdenum disulfide (MoS2) membrane and silicon nitride (SiNx) drumhead, and the effects of gas pressure on an MoS2 membrane resonator. Employing finite element simulations alongside theoretical modeling, the study thoroughly analyzes the coupling dynamics between MoS2 and SiNx resonators and investigates the vibrational responses of MoS2 membranes under pressure. Key achievements include the identification of vibrational modes, calculation of coupling constants, and comprehensive understanding of pressurized MoS2 membrane resonator behavior. These insights pave the way for enhancing NEMS applications in sensitive detection and resonant frequency modulation, significantly contributing to the field of nanotechnology and the development of advanced NEMS devices.

This thesis investigates the disparities in losses between 2D-based design simulations and a 3D realization of solenoidal inductors featuring distributed gaps. The inductor geometry entails a solenoidal copper winding enveloped by sintered ferrite rings and end caps, with the air gap required for energy storage distributed over multiple smaller discrete gaps. The simulated 3D structure possesses higher losses than its 2D cross-section due to inherent structural features. The research culminates in two contributions. First, a practical two-variable design approach is presented, leveraging matrix algebra to succinctly represent the decision quantities as functions of the two most important variables to the application. The procedure results yield several informative plots that assist in selecting a design that meets the efficiency and thermal limits. Second, a detailed explanation is provided on the 3D loss effects, along with the recommended design considerations and a method to estimate the dominant 3D loss effect using simple 2D simulations. The design recommendations address a 26-fold increase in the core loss of the outer ferrite rings. They also reduce the copper loss due to the termination effect by 55% using spacer ferrite layers. A simple 2D simulation method is proposed to accurately predict the increased 3D copper loss due to the axial shift of the winding to within 3% and runs 60 times faster than the equivalent 3D simulation. Additionally, a derived equation for the optimal turn spacing aligns with the simulation results with <6% error, offering practical insights for design optimization. These results enable the design of a low-loss solenoidal inductor and accurate loss estimations without running lengthy and complicated 3D simulations. A 13 µH, 150 Arms solenoidal inductor prototype for operation in a 10 kV-to-400 V, 50 kW converter cell serves as empirical validation, corroborating the efficacy of the proposed analysis and design methodology. / Master of Science / It is common to rely on a 2D cross-section of the structure to facilitate the design procedure for inductors, essential components used in electronic circuits to control and convert energy. Two-dimensional simulations of inductors are preferred due to their modeling simplicity, running speed, and low processing power requirement compared to 3D simulations. This thesis investigates the disparities in losses between 2D-based design simulations and a 3D realization of solenoidal inductors featuring distributed gaps. The inductor geometry entails a helical copper winding enveloped by rings and end caps made of a magnetic material. There are multiple small air gaps between the magnetic rings that are required for energy storage, and having multiple small gaps instead of a single large one is referred to as "distributed gaps". The simulated 3D structure possesses higher losses than its 2D cross-section due to inherent structural features. The research culminates in two contributions. First, a practical two-variable design approach is presented, leveraging matrix algebra to succinctly represent the decision quantities as functions of the two most important variables to the application. The procedure results yield several informative plots that assist in selecting a design that meets the efficiency and thermal limits. Second, a detailed explanation is provided on the 3D loss effects, along with the recommended design considerations and a method to estimate the dominant 3D loss effect using simple 2D simulations. The design recommendations address a 26-fold increase in the loss of the outer rings and reduce the copper loss by 55%. A simple 2D simulation method is proposed to accurately predict the increased 3D copper loss to within 3% and runs 60 times faster than the equivalent 3D simulation. Additionally, a derived equation for the optimal turn spacing aligns with the simulation results with <6% error, offering practical insights for design optimization. These results enable the design of a low-loss solenoidal inductor and accurate loss estimations without running lengthy and complicated 3D simulations. A 13 µH, 150 Arms solenoidal inductor prototype for operation in a 10 kV-to-400 V, 50 kW converter cell serves as empirical validation, corroborating the efficacy of the proposed analysis and design methodology.

This thesis presents the results of 67 ABAQUS elasto-plastic Riks ultimate strength analyses of cross-stiffened panels. These panels cover a wide range of typical geometries. Uniaxial compression is applied to the panels, and in some cases combined with lateral pressure. For eight of the panels full-scale experimental results are available, and these verified the accuracy of the ABAQUS results. The 67 ABAQUS results were then compared to the ultimate strength predictions from the computer program ULSAP. In all but 10 cases the ULSAP predicted strength is within 30% of the ABAQUS value, and in all but 4 cases the predicted failure mode also agrees with that of ABAQUS. In one case the ULSAP predicted ultimate strength is 51% below the experimental value, and so this case is studied in detail. The discrepancy is found to be caused by the method which ULSAP uses for panels that experience overall collapse initiated by beam-column-type failure. The beam-column method program ULTBEAM is used to predict the ultimate strength of the 61 panels that ULSAP predicts to fail due to overall collapse of the stiffeners and plating which may or may not be triggered by yielding of the plate-stiffener combination at the midspan (Mode III or III-1). ULTBEAM is found to give more accurate results than ULSAP for Mode III or III-1 failure. Future work is recommended to incorporate ULTBEAM into ULSAP to predict the ultimate strength of panels that fail in Mode III or III-1. / Master of Science

Ce travail porte sur la mise en forme des matériaux composites à matrice polymère renforcée par des fibres courtes dont les performances physiques et mécaniques sont directement reliées à la distribution spatiale et à l’orientation des renforts employés. Il se focalise sur l’étude des mécanismes de déformation se produisant au cours de l’écoulement de ces systèmes qui se comportent comme des suspensions de fibres non-newtoniennes. Le problème est abordé par une procédure originale combinant images 3D acquises en temps réel et simulations numériques avancées, réalisées à l’échelle des fibres. Dans le premier cas, des suspensions modèles avec fluide suspensif non-newtonien ont été déformées en compression dans des conditions confinées dans un microtomographe à rayons X synchrotron. Cette technique a permis l’acquisition en temps réel de clichés 3D à forte résolution spatiale de l’écoulement des suspensions. Dans le deuxième cas, un code de calculs éléments finis 3D a été utilisé, celui-ci étant capable de décrire finement des objets immergés dans des fluides non-newtoniens, par des level-sets et des techniques de remaillage anisotrope. La pertinence des simulations numériques dans les régimes de concentration dilués à semi-dilués a été jaugée par une comparaison expériences-simulations avancée.De là, dans le régime de concentration dilué, nous montrons que le confinement de l’écoulement et le comportement rhéofluidifiant du fluide suspensif ont une influence mineure sur la cinématique des fibres, si ces dernières sont suffisamment éloignées des plateaux de compression. Si ce prérequis n’est pas respecté, l’effet du confinement devient important. Des modifications au modèle heuristique d’haltère de la littérature ont été proposées pour corriger la cinématique de fibres. Dans le régime semi-dilué, des déviations de la cinématique de fibres sont également observées au cœur des suspensions. Ces déviations sont principalement liées aux interactions hydrodynamiques entre fibres suffisamment voisines. La cinématique des fibres prédite par le modèle de Jeffery et les approximations de champ affine sont mises en défaut. Dans le régime concentré, si l’évolution de l’orientation globale de la suspension est étonnamment bien décrite par l’équation de Jeffery, de très importantes fluctuations des champs de translation et de rotation des fibres sont observées à l’échelle des fibres. Celles-ci sont induites par les nombreux contacts entre fibres qui peuvent par ailleurs être correctement prédits par le modèle de tube. / This study focuses on the processing of short fibre-reinforced polymer composites. The physical and mechanical properties of these materials are mainly affected by the position and orientation distribution of fibres induced during their forming. Thus, we analysed the flow-induced micro-mechanisms that arose at the fibre scale during the forming stage of these complex systems which behave as non-Newtonian fibre suspensions. For that purpose, an original approach was developed by combining 3D imaging technique and direct numerical simulation, both performed at the fibre scale. Hence, several model fibre suspensions with a non-Newtonian suspending fluid and with a concentration regime that ranged from dilute to concentrated were prepared . They were subjected to confined lubricated compression loadings using a rheometer mounted on a synchrotron X-ray microtomograph. Thanks to very short scanning times, 3D images of the evolving fibrous microstructures at high spatial resolution were recorded in real-time. These experiments were also simulated using a dedicated Finite Element library enabling an accurate description of fibre kinematics in complex suspending fluids thanks to high performance computation, level sets and adaptive anisotropic meshing. The efficiency of the numerical simulation from the dilute to semi-dilute concentration regimes was assessed through experimental and numerical comparisons.Then, we showed that the confinement effect and the non-Newtonian rheology of the suspending fluid had a weak effect on the fibre kinematics, if the fibres were sufficiently far from the compression platens, typically the fibre-platen distance should be larger than twice the fibre diameter. Otherwise, confinement effects occurred. Some extensions of the dumbbell model were proposed to correct the fibre kinematics in this flow conditions. In semi-dilute concentration, deviations of the fibre kinematics compared to the Jeffery’s predictions were also observed and related to hydrodynamic interactions between fibres. In this case, the predictions of Jeffery’s model and the related assumption of affine fibre motions are less relevant. In the concentrated regime, even if the overall orientation of fibre suspension could be astonishingly well described by using the Jeffery’s model, strong fluctuations on each fibre motion and rotation were observed. These deviations were induced by the numerous fibre-fibre contacts, which could be correctly predicted by the tube model.

Doctor of Philosophy / Department of Chemistry / Takashi Ito / Self-organized nanoporous materials have drawn a lot of attention because the uniform, highly dense, and ordered cylindrical nanopores in these materials provide a unique platform for chemical separations and chemical sensing applications. Here, we explore self-organized nanopores of PS-b-PMMA diblock copolymer thin films and anodic gallium oxide for chemical separations and sensing applications. In the first study, cyclic voltammograms of cytochrome c on recessed nanodisk-array electrodes (RNEs) based on nanoporous films (11, 14 or 24 nm in average pore diameter; 30 nm thick) derived from polystyrene-poly(methylmethacrylate) diblock copolymers were measured. The faradic current of cytochrome c was observed on RNEs, indicating the penetration of cytochrome c (hydrodynamic diameter ≈ 4 nm) through the nanopores to the underlying electrodes. Compared to the 24-nm pores, the diffusion of cytochrome c molecules through the 11- and 14-nm pores suffered significantly larger hindrance. The results reported in this study will provide guidance in designing RNEs for size-based chemical sensing and also for controlled immobilization of biomolecules within nanoporous media for biosensors and bioreactors. In another study, conditions for the formation of self-organized nanopores of a metal oxide film were investigated. Self-organized nanopores aligned perpendicular to the film surface were obtained upon anodization of gallium films in ice-cooled 4 and 6 M aqueous H2SO4 at 10 V and 15 V. The average pore diameter was in the range of 18 ~ 40 nm, and the anodic gallium oxide was ca. 2 µm thick. In addition, anodic formation of self-organized nanopores was demonstrated for a solid gallium monolith incorporated at the end of a glass capillary. Nanoporous anodic oxide monoliths formed from a fusible metal will lead to future development of unique devices for chemical sensing and catalysis. In the final study, surface chemical property of self-organized nanoporous anodic gallium oxide is explored through potentiometric measurements. The nanoporous anodic and barrier layer gallium oxide structures showed slow potentiometric response only at acidic pH (≤ 4), in contrast to metallic gallium substrates that exhibited a positive potentiometric response to H⁺ over the pH range examined (3-10). The potentiometric response at acidic pH probably reflects some chemical processes between gallium oxide and HCl.