Zwei wesentliche Vorrausetzungen zum Aufbau mechanischer Verhaltensprognosen auf Basis der finiten-Element-Methode (FEM) sind die Verfügbarkeit von Materialmodellen sowie zugehörige Messverfahren zur Parameterbestimmung. Gegenstand dieser Abhandlung ist die Vorstellung einer neuartigen Messmethodik zur Erhebung des plastischen Biege- und Faltverhaltens von faserbasierten Verbundmaterialien und dessen Anwendung zum vereinfachten Aufbau von numerischen Struktursimulationen. Als besonderes Merkmal sei dabei der Ansatz einer äußeren, integralen Verhaltensbeschreibung der vielfältigen Vorgänge auf der Mikrostrukturebene des Materials genannt. Damit wird es möglich das mechanische Strukturverhalten komplexer Makrostrukturen, wie komplette Verpackungen auf Basis von Karton-Verbundmaterial, zu untersuchen und damit Optimierungen hinsichtlich Versagensverhalten und Materialeffizienz durchzuführen.

Das Innenhochdruck-Umformen (IHU), ein Verfahren der Metallformung zur Herstellung von anspruchsvollen Bauteilen mit komplexer Geometrie aus meist hohlzylindrischen Halbzeugen, wird in einigen Branchen seit mehreren Jahrzehnten mit großem Erfolg angewendet. Insbesondere die vielfältigen Applikationen aus dem Automotivbereich wie z.B. Elemente der Abgasanlage, Strukturbauteile oder auch Antriebselemente können hergestellt werden. Da die Trends der Rohr- und Blechumformung in Richtung Leichtbau, komplexer Bauteile mit geringen Ausbringungsmengen und hoher Genauigkeit gehen, ist perspektivisch mit der Erschließung weiterer Anwendungs-gebiete zu rechnen. Um das Verfahren effizienter zu gestalten, können zusätzliche Prozesse in das IHU-Verfahren integriert werden. Beispiele dafür sind das Lochen sowie das Kragenziehen und weitere Fügeprozesse. Typische Bauteile sind Leicht-baunockenwellen, bei denen die Nocken innerhalb des Umformprozesses auf die Rohre form- und kraftschlüssig gefügt werden. Ungeachtet einer beliebigen dreidimensionalen Formgebung und der hohen Flexibilität unterliegt das IHU-Verfahren gewissen Restriktionen. So werden im industriellen Umfeld generell nur Halbzeuge mit Wanddicken ab 1,5 mm bis maximal 3,5 mm umgeformt. Bei dünnwandigen, rohr-förmigen Bauteilen sind Wanddicken unter 1 mm üblich. Diese erfordern spezielle technologische Maßnahmen im Bereich des Werkzeugbaus insbesondere Anforderungen an Dichtsystem sowie Werkzeuggravur und unterliegen Prozessparametern mit entsprechend kleineren Prozessfenstern.

Hydroforming, a metal forming process for the production of sophisticated components with complex geometries from mostly tubular semi-finished products, has been successfully applied in some industries for several decades. Particularly, various applications from the automotive sector such as elements of the exhaust system, structural components or drive elements can be manufactured. As trends in tube and sheet metal forming move towards lightweight construction, complex components with low production volumes, and high precision, the prospective expansion into further application areas is anticipated. To enhance the efficiency of the process, additional processes can be integrated into the hydroforming process. Examples of this are punching, collar pulling and other joining processes. Typical components include lightweight camshafts in which the cams are form- and force-fitted onto the tubes within forming process. Despite arbitrary three-dimensional forming and the high degree of flexibility, the hydroforming process is subjected to certain restrictions. Generally, in an industrial environment, only semi-finished products with wall thicknesses from 1.5 mm to a maximum of 3.5 mm are formed. Wall thicknesses of less than 1 mm are common for thin-walled, tubular components. These require special technological measures in the area of toolmaking, particularly regarding sealing system and tool engraving, and are subjected to process parameters with correspondingly smaller process windows

The functional performance of joint implants is largely determined by the surface layer properties in contact. Wear/debris-induced osteolysis and aseptic loosening has been identified as the major cause of failure of metal-on-metal joint implants. A crucial requirement for the long-term stability of the artificial joint is to minimize the release of debris particles. Severe plastic deformation (SPD) processes have been used to modify the surface integrity properties by generating ultrafine, or even nano-sized grains and grain size gradients in the surface region of many materials. These fine grained materials often exhibit enhanced surface integrity properties and improved functional performance (wear resistance, corrosion resistance, fatigue life, etc.) compared with their conventional coarse grained counterparts. The aim of the present work is to investigate the effect of a SPD process, cryogenic burnishing, on the surface integrity modifications of a Co-Cr-Mo alloy, and the resulting wear performance of this alloy due to the burnishing-induced surface integrity properties. A systematic experimental study was conducted to investigate the influence of different burnishing parameters on distribution of grain size, phase structure and residual stresses of the processed material. The wear performance of the processed Co-Cr-Mo alloy was tested via pin-on-disk wear tests. The results from this work show that the cryogenic burnishing can significant improve the surface integrity of the Co-Cr-Mo alloy which would finally lead to advanced wear performance due to refined microstructure, high hardness, compressive residual stresses and favorable phase structure on the surface layer. A finite element model (FEM) was developed for predicting the grain size changes during burnishing of Co-Cr-Mo alloy under both dry and cryogenic conditions. A new material model was used for incorporating flow stress softening and associated grain size refinement caused by the dynamic recrystallization (DRX). The new material model was implemented in a commercial FEM software as a customized user subroutine. Good agreement between predictions and experimental observations was achieved. Encouraging trends are revealed with great potential for application in industry.

NiTi alloys have been the focus of Shape Memory Alloys (SMA) research and applications due their excellent ductility and shape memory properties, and these alloys have been extensively used in automotive, aerospace, and in biomedical applications. The effects of machining on the surface integrity and the corresponding material and mechanical properties of alloys can be best studied by utilizing NiTi alloys as workpiece material since their physical and mechanical properties are highly microstructure dependent. However, due to very poor machining performance of NiTi shape memory alloys, no comprehensive or systematic investigation on this topic has been conducted by researchers as yet. The current study makes a substantial and unique contribution to this area by making the first and significant contribution to studies on machining performance of NiTi shape memory alloys, and by achieving improved surface integrity and machining performance using cryogenic applications, which give significant reductions of tool-wear, cutting forces, and surface roughness. The influence of machining process conditions, including dry, MQL, preheated, cryogenic machining, and the effects of prefroze cryo machining on surface integrity characteristics such as microhardness, phase transformation, phase transformation temperature, depth of plastically deformed layer have been examined extensively, and unique findings have been obtained. The effects of machining process conditions, in particular preheated and cryogenic machining conditions, on thermo-mechanical and shape memory characteristics were identified through thermal cycling and stress-strain tests. For the first time, orthogonal cutting of NiTi shape memory alloys has been carried out in this study to investigate surface integrity comprehensively. Surface integrity and machining performance are compared for dry and prefroze cryogenic cooling conditions under a wide range of cutting speeds. Stress-induced martensitic phase transformation and deformation twinning were found in prefroze cryogenic and dry cutting conditions respectively. The existing microstructure-based constitutive models were used and modified to predict machining-induced phase transformation and resulting volume fraction. The modified model was implemented in commercial FEM software (DEFORM-2D) as a customized user subroutine. The obtained results from simulation and orthogonal cutting tests were compared considering martensitic volume fraction during cutting with various cutting speeds. The model captured the experimental trend of volume fraction induced by various cutting speeds and process variables. Overall, FEM simulation of cutting process of NiTi was successfully presented.

This study aims at the description, modelling and numerical prediction of ductile fracture in inelastic solids undergoing thermomechanical static or dynamic loading. Several research areas of contemporary interest in computer analysis of solids and structures are covered. The theoretical methodologies, computer implementations and practical applications will be treated. This thesis summarizes my recent research works since 1989 at the MSM Department of the University of Liège. However, it should also be useful to those who are interested in the most recent developments in finite element methods and in applying these techniques to the analysis of real industrial problems. Numerous references to original sources are included. For the convenience of the reader, each chapter of the thesis is designed to be self-contained, starts with a summary of the topic addressed, and finishes with an outline of the main results presented. Numerical examples are organized at the end of chapter 2 to 8 to assess the performance and applicability of the proposed mechanical and finite element models developed in each of them. Hereafter, a brief overview of the thesis is given. After a brief introduction in chapter 1, the numerical tools that are necessary to perform large strain thermomechanical static or dynamic analysis of solids are presented. In chapter 2, a general strategy for nonlinear dynamic finite element formulation is presented, including explicit and implicit time integration schemes. A special emphasis is placed on the application of high-speed metalforming and frictional contact-impact problems. Chapter 3 describes a strategy for solving problems involving transient thermal and thermomechanical analysis. A class of unified and mixed solid, thermal and coupled thermomechanical finite elements by assumed strain method is developed in chapter 4. Special care is taken to hourglass ans locking control. Once these developments are validated and their efficiency tested, it is then possible to tackle the problem of ductile fracture prediction and propagation. In chapter 5, a bibliographic research on the "local approach of ductile fracture" is presented. The implementation of six fracture criteria into various constitutive laws for predicting fracture initiation sites is also shown. A fully coupled elasto(-visco)-plastic damage model for isotropic material is developed in chapter 6. This model is based on irreversible thermodynamics theory and on the energy equivalence hypothesis. Chapter 7 presents the theoretical and experimental comparison for isotropic ductile material at fracture. Finally in chapter 8, the isotropic damage model of chapter 6 is extended to the case of anisotropic solids in which the damage growth itself is also anisotropic. The above developments have been implemented to an existing finite element code LAGAMINE developed since 1982 at the MSM Department of the University of Liège and are applied to many real engineering problems such as high speed rolling, magnetoforming, impact upsetting, dynamic forging, deep drawing of axisymmetric ans square cups, hot upsetting, warm folding of 3D sheet, non-isothermal hemispherical punch stretching, and other contact-impact examples.

This thesis is the result of the investigation and solution of a mechanicalproblem regarding flywheel malfunctions. A flywheel is, in short, a devicethat relies on a rotating object’s moment of inertia to store energy overshort time spans. This project is part of the development of a fourthflywheel prototype at the division for electricity at Uppsala university,which uses magnetic levitation to keep a hollow cylinder rotating at veryhigh speeds inside a vacuum chamber. Should the magnets fail however, orsome other error occur that leads to an uncontrolled state of rotation, thecylinder needs to be stabilized mechanically by a device usually referredto as ‘back-up bearing’. This contraption might, like an airbag of a car,never be used but needs to be included if an emergency occurs to protectother parts of the flywheel which would otherwise be destroyed by theunrestrained rotor. A theoretical pre-study was conducted to determine what challenges andrespective solutions the design of such a device would encounter, forexample the amount of energy in the rotor and possible ways to dissipate itin the event of a malfunction. The benefits and downsides of materials andmachine elements such as bearings were investigated in order to design aset of backup bearings. The modelling was done using SolidWorks, which wasalso used to conduct thermal and mechanical simulations on differentconcepts. MatLab was used for calculations, using formulae from themanufacturers and from different websites. The project concluded that the sheer energy of the flywheel at top speedpresents considerable thermodynamic difficulties. A solution capable ofhandling this was however achieved, albeit barely. Unfortunately onlysimulations and calculations confirm this result as no practicalexperiments could be conducted, therefore caution is advised in futureexperiments where the flywheel speed approaches maximum levels.

V této diplomové práci jsou popsané SHM metody používané v letectví a dále jsou udělány MKP simulace šíření ultrazvoukových vln v celokompozitním tenkostěnném materiálu používaném u leteckých konstrukcí. Pro simulaci byla zvolena SHM metoda nazývaná pitch-catch. Simulace byla provedena na dvou různých kompozitových materiálech a každý z nich byl testován třemí různými konfiguracemi s trhlinou a jednou konfigurací bez trhliny. Jako prepocessor byl použit MSC.Patran a jako post processory byli použity MSC.Nastran a MSC.Dytran, jejichž výsledky byli na závěr porovnány. Simulace prokázali, že rychlost šíření a amplituda vln šířících se v simulovaném panelu je trhlinami ovlivněna. Při konfiguracích s trhlinami rychlost šíření i amplituda vln byli menší, než v případě bez trhliny. Jako vhodnější post processor při MKP simulacích se ukázal MSC.Nastran, jehož výsledky byli přesnější a zárověň bylo i snažší správně odečítat hodnoty dat z grafů pro podrobnější pozorování šíření vln.

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