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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

ON FURTHER MODELING OF STIFFNESS AND DAMPING OF CORRUGATED CARDBOARDS FOR VIBRATION ISOLATION APPLICATION

2014 October 1900 (has links)
In a recent study, an environment-friendly material, corrugated cardboard, was used as a building block for the vibration isolator with a preliminary study. The present thesis was motivated to advance technology for improving the design of such a corrugated cardboard vibration isolator with a focus on the modeling of its stiffness and damping. In particular, this study has performed the following works: (1) improving the FE (finite element) model of the stiffness of the corrugated cardboards by more accurately identifying the material parameters in the cardboard material constitutive equation; (2) analyzing the effect of the error in geometry of the corrugated cardboards in the FE model; (3) developing the Rayleigh damping model of the corrugated cardboards and evaluating its accuracy. Several conclusions were drawn from this study: (1) the parameter identification procedure based on the inverse analysis is feasible for improving the accuracy of the model of the stiffness of the cardboard. (2) The FE model of the cardboards with a greater in-plane geometrical deflection has less vertical compressive stiffness. The geometrical deflections of the corrugated cardboards also change the condition of the contact friction stress and the compressive deformation. (3) Rayleigh damping model is accurate enough for calculating the damping of the corrugated cardboards. The contributions of the thesis include: (1) provision of a more accurate model for the compressive stiffness the corrugated cardboards, (2) finding that the friction between the cardboard and the vibrator and the geometrical error of the cardboards have a significant influence over the accuracy of the FE model, (3) finding that in practice the foregoing influence can significantly degraded the performance of the cardboards as a vibrator isolator, and (4) provision of a model for the compressive damping of the corrugated cardboards.
2

Influence de l’âge et du morphotype sur la réponse mécanique du thorax : étude expérimentale in vivo et analyse numérique à l'aide de modèles EF personnalisés du corps humain / Age and morphotype influence on thoracic mechanical response : in vivo experimental study and numerical analysis using personalized human body FE models

Poulard, David 19 December 2012 (has links)
Cette étude aborde le problème de l’aggravation du risque de fractures de côtes chez les automobilistesâgés en choc frontal. L’analyse de la bibliographie fait ressortir que les moyens actuels d’évaluationdu risque de fractures ne permettent pas de prendre en compte les différences anatomiques et depropriétés mécaniques du thorax observées chez les personnes âgées. Les modèles éléments finis (EF)personnalisés du corps humain offrent un grand potentiel en tant qu’outil avancé d’évaluation durisque de blessures. Toutefois, des données expérimentales sont nécessaires pour valider ces modèlesdans des conditions réalistes. De plus, le choix du niveau de personnalisation et la sensibilité de laréponse du modèle à celle-ci doivent être évaluées.Des expérimentations in vivo menés sur des volontaires ceinturés en choc léger, de différents âges etanthropométries, ont été réalisées. Ces tests ont permis d’étudier l’influence de l’âge et de lacorpulence sur la réponse mécanique du thorax et ont permis l’obtention de corridors nécessaires à lavalidation de modèles EF personnalisés. La géométrie du modèle numérique THUMS a été adaptée àcelle des volontaires et les propriétés mécaniques du thorax ont été modifiées au vu du vieillissementpour effectuer une analyse similaire dans le domaine lésionnel. Les simulations numériques ont mis enévidence un risque accru de fracture de côtes pour certains modèles personnalisés.Cette étude devrait permettre de mieux estimer le risque de blessure pour les automobilistesvulnérables. Elle devrait contribuer ainsi à promouvoir les modèles personnalisés du corps humaincomme outil avancé d’évaluation du risque de blessures. / This study deals with the topic of increased risk of rib fractures among elderly drivers infrontal impact. The analysis of the literature reveals that actual thorax injury assessment tools do nottake into account for the differences in anatomical features and biological material properties observedbetween adults and elderly. Personalized human body finite element (FE) models have great potentialas improved thorax injury assessment tools. However, experimental data are needed to validate thesemodels under real-world conditions. In addition, the choice of the level of personalization of the modeland the sensibility of the model response to this personalization must be assessed to predict thoracicinjury risk.In vivo sled tests were performed on belted volunteers of various anthropometries and age. These testswere used to assess the influence of age and corpulence on thorax mechanical response and allowed toobtain corridor responses needed to validate personalized FE models. The geometry of the FE modelTHUMS was adapted to the volunteers and the thorax material properties were modified consideringaging to carry out a similar analysis in the injurious domain. Numerical simulations highlighted anincreased risk of rib fractures for specific personalized models.This study should help to better estimate the injury risk for car occupants. It should contribute topromote personalized human body models as attractive thorax injury assessment tool ofvulnerable individuals.
3

Criteria for Machinability Evaluation of Compacted Graphite Iron Materials : Design and Production Planning Perspective on Cylinder Block Manufacturing

Berglund, Anders January 2011 (has links)
The Swedish truck industry is looking for new material solutions to achieve lighter engines with increased strength to meet customer demands and to fulfil the new regulations for more environmentally friendly trucks. This could be achieved by increasing the peak pressure in the cylinders. Consequently, a more efficient combustion is obtained and the exhaust lowered. This, however, exposes the engine to higher loads and material physical properties must therefore be enhanced. One material that could meet these demands is Compacted Graphite Iron (CGI). Its mechanical and physical properties make it ideal as cylinder block material, though there are drawbacks concerning its machinability as compared to other materials that are commonly used for the same purpose. Knowledge about machining of the material and its machinability is consequently inadequate. The main goal of this thesis is to identify and investigate the effect of the major factors and their individual contributions on CGI machining process behaviour. When the relationship between the fundamental features; machinability, material microstructure, and material physical properties, are revealed, the CGI material can be optimized, both regarding the manufacturing process and design requirements. The basic understanding of this is developed mainly through experimental analysis as, e.g., machining experiments and material characterization. The machining model presented in this thesis demonstrates the influence of material and process parameters on CGI machinability. It highlights machinability from both design and production planning perspectives. Another important objective of the thesis is an inverse thermo−mechanical FE model for intermittent machining of CGI. Here, experimental results obtained from a developed simulated milling method are used as input data, both to calibrate and validate the model. With these models, a deeper understanding is obtained regarding the way to achieve a stable process, which is the basis for future optimization procedures. The models can therefore be used as a foundation for the optimization of CGI component manufacturing. / <p>QC 20111121</p> / MERA - OPTIMA CGI / FFI - OPTIMA phase two
4

Investigation of Polymer packaging films behavior subjected to tension and tearing

MADDALA, PRANAY RAJ REDDY January 2017 (has links)
The course of polymer film functioning has been a crucial concern in the advent of packaging technology. The thesis project aims towards obtaining an understanding of mechanical properties for a class of these materials, namely LDPE and PET. A constitutive understanding of this behavior in the case of LDPE is acquired through incorporating a plastic stress strain relationship in an iterative approach with focus put on the sensitivity of a few parameters by following a simple linear curve-fit technique in a way that the global as well as the local response are predictable. FE-models also developed in this way are validated with experimental data. An inverse analysis testing validity or usefulness of DIC technique in identifying a material model is done and some discussions are drawn towards this area. A relative numerical study with respect to experimentally obtained global response for tearing of these polymers is done through use of a similar material model developed from tensile tests and the challenges faced in this area have been addressed.
5

Modelling of friction stir spot welding

Reilly, Aidan January 2013 (has links)
Friction stir spot welding (FSSW) is a solid-state welding process which is especially useful for joining precipitation-hardened aluminium alloys that undergo adverse property changes during fusion welding. It also has potential as an effective method for solid-state joining of dissimilar alloys. In FSSW, heat generation and plastic flow are strongly linked, and the scale of the process in time and space is such that it is difficult to separate and control the influence of all the relevant input parameters. The use of modelling is well-established in the field of welding research, and this thesis presents an analysis of the thermal and mechanical aspects of FSSW, principally using the finite element (FE) technique. Firstly, a thermal FE model is shown, which is subsequently validated by reference to experimental temperature data in both aluminium-to-aluminium and aluminium-to-steel welds. Correlations between high-quality welds and temperature fields are established, and predictions are made for peak temperatures reached under novel welding conditions. Deformation and heating are strongly linked in FSSW, but existing modelling tools are poorly suited to modelling flow processes in the conditions extant in FSSW. This thesis discusses the development and optimisation of two novel techniques to overcome the limitations of current approaches. The first of these uses greatly simplified constitutive behaviour to convert the problem into one defined purely by kinematics. In doing so, the boundary conditions reduce to a small number of assumptions about the contact conditions between weld material and tool, and the model calculation time is very rapid. This model is used to investigate changes in the slip condition at the tool to workpiece interface without an explicit statement of the friction law. Marker experiments are presented which use dissimilar composition but similar strength alloys to visualise flow patterns. The layering behaviour and surface patterns observed in the model agree well with observations from these experiments. The second approach extends the FE method to include deformation behaviour without the need for a fully-coupled approach, guided by the kinematic model. This is achieved using an innovative sequential small-strain analysis method in which thermal and deformation analyses alternate, with each running at a very different timescale. This technique avoids the requirement to either remesh the model domain at high strains or to use an explicit integration scheme, both of which impose penalties in calculation time and model complexity. The method is used to relate the purely thermal analysis developed in the work on thermal modelling to welding parameters such as tool speed. The model enables predictions of the spatial and temporal evolution of heat generation to be made directly from the constitutive behaviour of the alloy and the assumed velocity profile at the tool-workpiece interface. Predictions of the resulting temperature history are matched to experimental data and novel conditions are simulated, and these predictions correlate accurately with experimental results. Hence, the model is used to predict welding outcomes for situations for which no experimental data exists, and process charts are produced to describe optimum welding parameters. The methods and results presented in this thesis have significant implications for modelling friction stir spot welding, from optimising process conditions, to integration with microstructural models (to predict softening in the heat-affected zone, or the formation of intermetallics at the interface in dissimilar welds). The technique developed for sequential small strain finite element analysis could also be investigated for use in other kinematically constrained solid-state friction joining processes.
6

Simulation Study of Epitaxially Regrown Vertical-Cavity Surface-Emitting Lasers

Wu, Xiaoyue January 2011 (has links)
The vertical-cavity surface-emitting laser or VCSEL is a special type of diode laser, which has established itself in optoelectronic applications asa low-cost, high-quality miniaturized light source. The development of VCSELs can be largely promoted with support from computer simulations. In this study, we have used such simulations, on one hand to understand and improve the VCSEL performance, and on the other hand to prepare for analyzing new device concepts such as transistor-VCSELs. This thesis starts with a background introduction to the principle idea of VCSELs and then states the significance of this simulation work.Then it briefly introduces the previously used simulation workbench Sentaurus and explains the mathematical approach and the computation methods of the finally chosen simulator PICS3D. The case study of a fabricated and characterized epitaxially regrown VCSEL is the major component of this work. First the device configuration is demonstrated with detailed discussion on several design features. Second the physical models of electrical, optical and thermal phenomena along with their key parameters are presented and so are the advanced models for the active region. The main results of simulation, including steady-state characteristics and small-signal modulation, show good agreement with the experimental results and reveal some imperfections of the device design and processing, such as the overestimated stability of the regrown junction and the variation of cavity length caused by over-etch. This work is also treated as an evaluation of the simulator PICS3D, and two problems are identified: one is the troublesome way to construct a 3D device by coupling several 2D layer structures together, requiring the mesh for each layer structure to be compatible; the other would be the tricky boundary setting for the adopted method, Effective Index Method (EIM), for the transverse field calculation when only a weak index guiding effect exits in the cavity. Finally, we summarize this work and suggest some tasks for further simulations.
7

Experimental Study And Modeling Of Mechanical Micro-machining Of Particle Reinforced Heterogeneous Materials

Liu, Jian 01 January 2012 (has links)
This study focuses on developing explicit analytical and numerical process models for mechanical micro-machining of heterogeneous materials. These models are used to select suitable process parameters for preparing and micro-machining of these advanced materials. The material system studied in this research is Magnesium Metal Matrix Composites (Mg-MMCs) reinforced with nano-sized and micro-sized silicon carbide (SiC) particles. This research is motivated by increasing demands of miniaturized components with high mechanical performance in various industries. Mg-MMCs become one of the best candidates due to its light weight, high strength, and high creep/wear resistance. However, the improved strength and abrasive nature of the reinforcements bring great challenges for the subsequent micro-machining process. Systematic experimental investigations on the machinability of Mg-MMCs reinforced with SiC nano-particles have been conducted. The nanocomposites containing 5 Vol.%, 10 Vol.% and 15 Vol.% reinforcements, as well as pure magnesium, are studied by using the Design of Experiment (DOE) method. Cutting forces, surface morphology and surface roughness are characterized to understand the machinability of the four materials. Based on response surface methodology (RSM) design, experimental models and related contour plots have been developed to build a connection between different materials properties and cutting parameters. Those models can be used to predict the cutting force, the surface roughness, and then optimize the machining process. An analytical cutting force model has been developed to predict cutting forces of MgMMCs reinforced with nano-sized SiC particles in the micro-milling process. This model is iv different from previous ones by encompassing the behaviors of reinforcement nanoparticles in three cutting scenarios, i.e., shearing, ploughing and elastic recovery. By using the enhanced yield strength in the cutting force model, three major strengthening factors are incorporated, including load-bearing effect, enhanced dislocation density strengthening effect and Orowan strengthening effect. In this way, the particle size and volume fraction, as significant factors affecting the cutting forces, are explicitly considered. In order to validate the model, various cutting conditions using different size end mills (100 µm and 1 mm dia.) have been conducted on Mg-MMCs with volume fraction from 0 (pure magnesium) to 15 Vol.%. The simulated cutting forces show a good agreement with the experimental data. The proposed model can predict the major force amplitude variations and force profile changes as functions of the nanoparticles’ volume fraction. Next, a systematic evaluation of six ductile fracture models has been conducted to identify the most suitable fracture criterion for micro-scale cutting simulations. The evaluated fracture models include constant fracture strain, Johnson-Cook, Johnson-Cook coupling criterion, Wilkins, modified Cockcroft-Latham, and Bao-Wierzbicki fracture criterion. By means of a user material subroutine (VUMAT), these fracture models are implemented into a Finite Element (FE) orthogonal cutting model in ABAQUS/Explicit platform. The local parameters (stress, strain, fracture factor, velocity fields) and global variables (chip morphology, cutting forces, temperature, shear angle, and machined surface integrity) are evaluated. Results indicate that by coupling with the damage evolution, the capability of Johnson-Cook and Bao-Wierzbicki can be further extended to predict accurate chip morphology. Bao-Wierzbiki-based coupling model provides the best simulation results in this study. v The micro-cutting performance of MMCs materials has also been studied by using FE modeling method. A 2-D FE micro-cutting model has been constructed. Firstly, homogenized material properties are employed to evaluate the effect of particles’ volume fraction. Secondly, micro-structures of the two-phase material are modeled in FE cutting models. The effects of the existing micro-sized and nano-sized ceramic particles on micro-cutting performance are carefully evaluated in two case studies. Results show that by using the homogenized material properties based on Johnson-Cook plasticity and fracture model with damage evolution, the micro-cutting performance of nano-reinforced Mg-MMCs can be predicted. Crack generation for SiC particle reinforced MMCs is different from their homogeneous counterparts; the effect of micro-sized particles is different from the one of nano-sized particles. In summary, through this research, a better understanding of the unique cutting mechanism for particle reinforced heterogeneous materials has been obtained. The effect of reinforcements on micro-cutting performance is obtained, which will help material engineers tailor suitable material properties for special mechanical design, associated manufacturing method and application needs. Moreover, the proposed analytical and numerical models provide a guideline to optimize process parameters for preparing and micro-machining of heterogeneous MMCs materials. This will eventually facilitate the automation of MMCs’ machining process and realize high-efficiency, high-quality, and low-cost manufacturing of composite materials.
8

Preliminary Analysis of an Internal Annuloplasty Ring for the Aortic Valve

Sadeghi Malvajerdi, Neda January 2017 (has links)
Among the four valves of the heart, the aortic valve (AV) is frequently affected by disease. When progressive dilatation of the valve produces a leak when the valve should close (regurgitation), repair may be possible. AV repair is a desirable option because, contrary to AV replace-ment using a prosthesis, it does not require life-long anticoagulation treatment, and retains the original tissues that naturally combat structural degradation. All the AV repair procedures developed by cardiac surgeons require a good stabilization of the ventriculo-aortic junction (VAJ) diameter, through annuloplasty or reimplantation, for long-term success. In the present work, a preliminary design for a new type of annuloplasty ring is proposed that surgeons could tailor to the each valve’s shape and suture inside the VAJ. The design consists in wrapping a commonly available surgical biomaterial into a ring of controlled radial flexibility. For sizing and material selection, several models of increasing complexity were created to account for the anisotropic, hyperelastic nature of all the materials involved. First, an analytical model was programmed in MATLAB to assess the radial flexibility of annuloplasty rings formed with different biomaterials and select those that could match the physiological VAJ radial flexibility between systolic and diastolic pressures. The same program was also used to reproduce the experimental radial and longitudinal stretches of the human VAJ from 0 to 140 mmHg pressures. The analytical models were used to calibrate the parameters of independent finite element (FE) models of the VAJ and ring. Finally, the FE approach was extended to simulate the ring after suturing inside the VAJ, to determine the radial flexibility of the assembly under pulsatile pressure. Supple Peri-Guard® bo-vine pericardium patches used in transverse orientation emerged as the best currently available material option for the proposed ring, although a material providing more physiological radial flexibility would be desirable.
9

Non-Linear strain paths in Sheet Metal Forming

Eriksson, Anton January 2021 (has links)
Today's automotive requirements have resulted in complex Sheet Metal Forming (SMF) processes of Sheet Metal (SM) with reduced formability, and thus it is crucial to be able to predict formability accurately to prevent material failure during SMF. Formability predictions today utilize Forming Limit Curves (FLC)s in Finite Element Analysis (FEA), but  FLCs are not valid for the Non-Linear Strain Paths (NLSP)s generated during SMF. One purpose of this thesis is thus to increase the knowledge on FP handling NLSP,  which was obtained through providing suggestions of failure models for handling NLSP effects, based upon literature on the subject. Generating NLSP experimentally is both time and material costly with the conventional method, thus the second purpose of this thesis was to increase the knowledge on test procedures for generating NLSP in SM. Based upon the findings of Chandramohan \cite{chandramohan_study_2021} five test procedures for generating NLSP were put forward, and the Nakajima test with modified punch geometry was chosen for further study.   In this thesis, the NLSP characteristics of two modified punch geometries were evaluated by FEA performed using LS-DYNA. For the FEA three specimens with blank width of 50, 100 and 200 mm was used, and the anisotropic Barlat yld2000  was used as the material model. This material model was calibrated to material data of Mild steel CR4, Aluminium alloy AA6016, and Dual-phase steel DP800. The results for all materials showcased similar reacquiring general NLSP characteristics at the corners of the punch features, which are unfavorable positions when failure by necking is evaluated, and thus it was concluded that the tested punch geometries are not favorable and more development of the punch geometry is needed. / Dagens fordonskrav, har lett till komplexa plåtformnings processer av plåtmaterial med reducerad formbarhet, och det är därför väsenligt att kunna förutsäga formbarhet noggrant för att förhindra materialbrott under plåtformning. Försträckning och brott förutses idag genom Formgränskurvor (FGK) i finita element analyser (FEA), men dessa gäller inte för icke-linjära töjningsvägar som uppkommer under plåtformning. Ett syfte av denna avhandling är därför att öka kunskapen kring modeller för att förutsäga formbarhet under icke-linjära töjningsbanors effekter, vilket uppnådes genom att  presenteras  förslag på brott modeller för att hantera de icke-linjära töjningsvägar baserade på  literatur inom området. Att generera icke-linjära töjningsvägar experimentellt är både tids och materialkrävande med den konventionella metoden, således är det andra syftet av denna avhandling att öka kunskapen kring test metoder för att generera icke-linjär töjningsbvägar i plåt. Baserat på Chandramohans \cite{chandramohan_study_2021} resultat diskuteras fem test procedurer för att generera icke-linjära töjningsvägar, och Nakajima test med modifierad stämpelgeometri valdes för vidare studie.  I denna avhandling studerades töjningsignaturen av två stämpelgeometrier med FEA i LS-DYNA. Till FEA:n användes tre ämnen med bredd av 50, 100 och 200mm, och anisotropiska Barlat yld2000 användes som materialmodell. Denna materialmodell kalibrerades mot experimentella mätvärden för mjukt stål CR4, Aluminiumlegering AA6016 och Stål DP800. Resultaten visade för alla material återkommande generella icke-linjära töjningsbanor enbart för hörnorna på stansgeometrierna, vilket är icke önskvärda positioner då brott pga. midjebildning utvärderas, och således drogs slutsatsen att nuvarande stansgeometri inte är gynnsam och ytterligare utveckling behövs.
10

Rehabilitation of Exterior RC Beam-Column Joints using Web-Bonded FRP Sheets

Mahini, Seyed Saeid Unknown Date (has links)
In a Reinforced Concrete (RC) building subjected to lateral loads such as earthquake and wind pressure, the beam to column joints constitute one of the critical regions, especially the exterior ones, and they must be designed and detailed to dissipate large amounts of energy without a significant loss of, strength, stiffness and ductility. This would be achieved when the beam-column joints are designed in such a way that the plastic hinges form at a distance away from the column face and the joint region remain elastic. In existing frames, an easy and practical way to implement this behaviour following the accepted design philosophy of the strong-column weak-beam concept is the use a Fibre Reinforced Plastic (FRP) retrofitting system. In the case of damaged buildings, this can be achieved through a FRP repairing system. In the experimental part of this study, seven scaled down exterior subassemblies were tested under monotonic or cyclic loads. All specimens were designed following the strong-column weak-beam principal. The three categories selected for this investigation included the FRP-repaired and FRP-retrofitted specimens under monotonic loads and FRP-retrofitted specimen under cyclic loads. All repairing/retrofitting was performed using a new technique called a web-bonded FRP system, which was developed for the first time in the current study. On the basis of test results, it was concluded that the FRP repairing/retrofitting system can restore/upgrade the integrity of the joint, keeping/upgrading its strength, stiffness and ductility, and shifting the plastic hinges from the column face toward the beam in such a way that the joint remains elastic. In the analytical part of this study, a closed-form solution was developed in order to predict the physical behaviour of the repaired/retrofitted specimens. Firstly, an analytical model was developed to calculate the ultimate moment capacity of the web-bonded FRP sections considering two failure modes, FRP rupture and tension failure, followed by an extended formulation for estimating the beam-tip displacement. Based on the analytical model and the extended formulation, failure mechanisms of the test specimens were implemented into a computer program to facilitate the calculations. All seven subassemblies were analysed using this program, and the results were found to be in good agreement with those obtained from experimental study. Design curves were also developed to be used by practicing engineers. In the numerical part of this study, all specimens were analysed by a nonlinear finite element method using ANSYS software. Numerical analysis was performed for three purposes: to calculate the first yield load of the specimens in order to manage the tests; to investigate the ability of the web-bonded FRP system to relocate the plastic hinge from the column face toward the beam; and to calibrate and confirm the results obtained from the experiments. It was concluded that numerical analysis using ANSYS could be considered as a practical tool in the design of the web-bonded FRP beam-column joints.

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