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Ferroelektroelastische Keramiken besitzen aufgrund ihrer elektromechanischen Koppeleigenschaften Bedeutung in der Sensorik und Aktuatorik. Zur Vorhersage der Bauteileigenschaften und Beurteilung der Bauteilfestigkeit werden Materialmodelle benötigt. In der vorliegenden Arbeit wird ein mehrachsiges, ratenunabhängiges Materialmodell für ferroelektroelastische Keramiken einschließlich der zur effizienten Lösung notwendigen numerischen Methoden ausgearbeitet. Dabei erfolgt die Einbeziehung von Ansätzen aus der makroskopischen phänomenologischen und mikroelektromechanischen phänomenologischen Modellierung. Das resultierende Materialmodell stellt einen Versuch dar, die Vorteile beider Betrachtungsweisen zu vereinen und trägt deshalb die Bezeichnung "hybrid". In einem ersten Beispiel wird gezeigt, dass das hybride Materialmodell die für Barium-Titanat-Keramiken experimentell beobachtete Materialantwort reproduzieren kann. In einem zweiten Beispiel erfolgt die Anwendung auf morphotrope PZT-Keramiken. Dabei wird die in jüngerer Vergangenheit entdeckte monokline Phase zusammen mit der elektronenmikroskopisch beobachteten hierarchischen Struktur von Mikro- und Nanodomänen in vereinfachter Weise berücksichtigt. Auf Grundlage der getroffenen Modellannahmen gelingt es, die experimentell gemessene makroskopische Materialantwort der morphotropen PZT-Keramik PIC151 (PI Ceramic GmbH, Lederhose, Deutschland) für ausgewählte Lastfälle mit guter Genauigkeit vorherzusagen. / Ferroelectroelastic ceramics are used in sensor and actuator applications due to their electromechanical coupling properties. In order to predict the behavior of components or to assess their strength, material models are required. In the present work, a multi-axial, rate-independent material model for ferroelectroelastic ceramics is elaborated. This includes the development of efficient numerical solution methods. By incorporating ideas from known macroscopic phenomenological and micro-electromechanical phenomenological models into the novel model, it is attempted to combine the advantages of both approaches. In a first example, it is shown that the hybrid model can reproduce the experimentally observed material response of barium titanate ceramics. In a second example, the model is applied to morphotropic PZT ceramics. In this context, the recently discovered monoclinic phase as well as the hierarchical structure of micro-domains and nano-domains observed by means of electron microscopy are taken into account in a simplified way. Based on the assumptions made, the experimentally measured material response of the morphotropic PZT ceramic PIC151 (PI Ceramic GmbH, Lederhose, Germany) is predicted with reasonable accuracy for selected load cases.

Aluminum and steel components are usually quenched in forced gas, oil or water flow to improve mechanical properties and improve product life. During the quenching process, heat is transferred rapidly from the hot metal component to the quenchant and the rapid temperature drop introduces phase transformation and deformation in the hot metal component. As a result, quenching problems arise such as distortion, cracking and high tensile residual stresses. To avoid or minimize these problems while improving mechanical properties, process optimization is needed for both part geometry and quenching process design. A series of methods, including four existing methods and two new methods developed in this dissertation, were applied to obtain accurate thermal boundary conditions, i.e., the heat transfer coefficient (HTC) distribution. The commercially available material model DANTE was applied with finite element software ABAQUS to model the phase transformations and constitutive behavior of steel parts during quenching. A user material subroutine was developed for aluminum alloys based on a constitute model and tensile test data. The predicted residual stresses in the quenched parts agreed with those measured using the improved resistance strain gauge hole-drilling method and other methods, which validates the numerical models.

A popular way to reduce weight in industrial products without compromising the strength or stiffness is to replace components made of metal by plastics that have been reinforced by glass fibers. When fibers are introduced in a plastic, the resulting composite usually becomes anisotropic, which makes it much more complex to work with in simulation software. This thesis looks at modeling of such a composite using the multi-scale material modeling tool Digimat. An injection molding simulation of a brush cutter casing made of a short fiber reinforced plastic has been performed in order to obtain information about the glass fiber orientations, and thus the anisotropy, in each material point. That information has then been transferred over from the injection mesh to the structural mesh via a mapping routine. An elasto-viscoplastic material model with failure has been employed and calibrated against experimental data to find the corresponding material parameters. Lastly, a finite element analysis simulating a drop test has been performed. The results from the analysis have been compared with a physical drop test in order to evaluate the accuracy of the methodology used. The outcome has been discussed, conclusions have been drawn and suggestions for further studies have been presented.

The report aims to describe the austenitic stainless steel Sanicro 25 from a thermomechanical point of view. The thermal and mechanical properties of the material make it suitable for use in coal – and thermal power plants. By the use of Sanicro 25 it would be possible to bring the efficiency of these plants up while bringing the carbon emissions down.A material model is created from material testing and validated through simulation in the finite element software Abaqus. The model that has been derived describes the material behavior during loading and stress relaxation for the first cycle in a thermomechanical fatigue test well. The unloading part of the cycle however cannot be described correctly by the use of this model. / Rostfritt

This thesis utilizes the Immersed Interface Finite Element Method (IIFEM) for shape optimization and material design, while also investigating the modeling and parameterization of lung tissue for Diver Underwater Explosion (UNDEX) simulations. In the first part, a shape optimization scheme utilizing a four-noded rectangular immersed-interface element is presented. This method eliminates the need for interface fitted mesh or mesh morphing, reducing computational costs while maintaining solution accuracy. Analytical design sensitivity analysis is performed to obtain gradients for the optimization formulation, and various parametrization techniques are explored. The effectiveness of the approach is demonstrated through verification and case studies. For material design, the study combines topological shape optimization with IIFEM, providing a computational approach for architecting materials with desired effective properties. Numerical homogenization evaluates effective properties, and level set-based topology optimization evolves boundaries within the unit cell to generate optimal periodic microstructures. The design space is parameterized using radial basis functions, facilitating a gradient-based optimization algorithm for optimal coefficients. The method produces geometries with smooth boundaries and distinct interfaces, demonstrated through numerical examples. The thesis then delves into modeling the mechanical response of lung tissues, particularly focusing on hyperelastic and hyperviscoelastic models. The research adopts a phased approach, emphasizing hyperelastic model parametrization while reserving hyperviscoelastic model parametrization for future studies. Alternative methods are used for parametrization, circumventing direct experimental tests on biological materials. Representative material properties are sourced from literature or refit from existing experimental data, incorporating both empirically derived data and practical values suitable for simulations. Damage parameter quantification relies on asserted quantitative relationships between injury levels and the regions or percentages of affected lung tissue. / Doctor of Philosophy / This research explores the following themes: optimizing shapes, designing materials using repetitive identical building blocks, and understanding how divers' lungs respond to underwater explosions. When computationally analyzing structures with multiple materials, the conventional method involves creating meshes that align with material interfaces, which can be intricate and time-consuming. The Immersed Interface Finite Element Method (IIFEM) is introduced as a computational approach that simplifies this process, utilizing a uniform grid for analysis regardless of interface shape. Consider a plate with a hole or other inclusions. Shape optimization seeks the optimal hole/inclusion shape for withstanding specific loading. Traditional optimization processes necessitate iterative mesh recreation, a step circumvented by employing IIFEM. This technique also extends to creating micro-building blocks of materials, enabling the architectural design of materials with desired qualities. Materials with specific properties, like strength or flexibility can be achieved. This thesis also addresses the challenge of understanding how divers' lungs respond to underwater explosions, a crucial aspect of safety. Advanced computer models are used to mimic the behavior of lung tissue under shock loads. Directly testing materials and tissues can be difficult and restricted. Techniques like gathering data from scientific papers and refitting existing experimental data are utilized to obtain the information needed. Also, it is hard to directly measure how much damage an underwater explosion does to a diver's lungs. Thus, the level of damage was quantified based on assertions about the relationship between different injury severities and how much lung tissue is affected.

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Micro-Powder Injection Moulding (Micro-PIM) technology is one of the key technologies that permit to fit with the increasing demands for smaller parts associated to miniaturization and functionalization in different application fields. The thesis focuses first on the elaboration and characterization of polymer-powder mixtures based on 316L stainless steel powders, and then on the identification of physical and material parameters related to the sintering stage and to the numerical simulations of the sintering process. Mixtures formulation with new binder systems based on different polymeric components have been developed for 316L stainless steel powders (5 µm and 16 µm). The characterization of the resulting mixtures for each group is carried out using mixing torque tests and viscosity tests. The mixture associated to the formulation comprising polypropylene + paraffin wax + stearic acid is well adapted for both powders and has been retained in the subsequent tests, due to the low value of the mixing torque and shear viscosity. The critical powder volume loading with 316L stainless steel powder (5 µm) according to the retained formulation has been established to 68% using four different methods. Micro mono-material injection (with 316L stainless steel mélange) and bi-material injection (with 316L stainless steel mélange and Cu mélange) are properly investigated. Homogeneity tests are observed for mixtures before and after injection. A physical model well suited for sintering stage is proposed for the simulation of sintering stage. The identification of physical parameters associated to proposed model are defined from the sintering stages in considering 316L stainless steel (5 µm)mixtures with various powder volume loadings (62%, 64% and 66%). Beam-bending tests and free sintering tests and thermo-Mechanical-Analyses (TMA) have also investigated. Three sintering stages corresponding to heating rates at 5 °C/min, 10 °C/min and 15 °C/min are used during both beam-bending tests and free sintering tests. On basis of the results obtained from dilatometry measurements, the shear viscosity module G, the bulk viscosity module K and the sintering stress σs are identified using Matlab® software. Afterwards, the sintering model is implemented in the Abaqus® finite element code, and appropriate finite elements have been used for the support and micro-specimens, respectively. The physical material parameters resulting from the identification experiments are used to establish the proper 316L stainless steel mixture, in combination with G, K and σs parameters. Finally, the sintering stages up to 1200 °C with three heating rates (5 °C/min, 10 °C/min and 15 °C/min) are also simulated corresponding to the four micro-specimen types (powder volume loading of 62%, 64% and 66%). The simulated shrinkages and relative densities of the sintered micro-specimens are compared to the experimental results indicating a proper agreement