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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.
21

Potential and application fields of lightweight hydraulic components in multi-material design

Ulbricht, Andreas, Gude, Maik, Barfuß, Daniel, Birke, Michael, Schwaar, Andree, Czulak, Andrzej 02 May 2016 (has links) (PDF)
Hydraulic systems are used in many fields of applications for different functions like energy storage in hybrid systems. Generally the mass of hydraulic systems plays a key role especially for mobile hydraulics (construction machines, trucks, cars) and hydraulic aircraft systems. The main product properties like energy efficiency or payload can be improved by reducing the mass. In this connection carbon fiber reinforced plastics (CFRP) with their superior specific strength and stiffness open up new chances to acquire new lightweight potentials compared to metallic components. However, complex quality control and failure identification slow down the substitution of metals by fiber-reinforced plastics (FRP). But the lower manufacturing temperatures of FRP compared to metals allow the integration of sensors within FRP-components. These sensors then can be advantageously used for many functions like quality control during the manufacturing process or structural health monitoring (SHM) for failure detection during their life cycle. Thus, lightweight hydraulic components made of composite materials as well as sensor integration in composite components are a main fields of research and development at the Institute of Lightweight Engineering and Polymer Technology (ILK) of the TU Dresden as well as at the Leichtbau-Zentrum Sachsen GmbH (LZS).
22

Dimensioning of Punctiform Metal-Composite Joints: A Section-Force Related Failure Criterion

Seidlitz, Holger, Ulke-Winter, Lars, Gerstenberger, Colin, Kroll, Lothar 20 April 2015 (has links) (PDF)
Reliable line production processes and simulation tools play a central role for the structural integration of thermoplastic composites in advanced lightweight constructions. Provided that material- adapted joining technologies are available, they can be applied in heavy-duty multi-material designs (MMD). A load-adapted approach was implemented into the new fully automatic and faulttolerant thermo mechanical flow drill joining (FDJ) concept. With this method it is possible to manufacture reproducible high strength FRP/metal-joints within short cycle times and without use of extra joining elements for the first time. The analysis of FDJ joints requires a simplified model of the joint to enable efficient numerical simulations. The present work introduces a strategy in modeling a finite-element based analogous-approach for FDJ-joints with glass fiber reinforced polypropylene and high-strength steel. Combined with a newly developed section-force related failure criterion, it is possible to predict the fundamental failure behavior in multi-axial stress states. The functionality of the holistic approach is illustrated by a demonstrator that represents a part of a car body-in-white structure. The comparison of simulated and experimentally determined failure loads proves the applicability for several combined load cases.
23

Topologically close-packed phase prediction in Ni-based superalloys : phenomenological structure maps and bond-order potential theory

Seiser, Bernhard Josef January 2011 (has links)
Single crystal nickel-based superalloys are used in modern gas turbines because of their remarkable resistance to creep deformation at elevated temperatures, which is ensured by the addition of significant amounts of refractory elements. Too high concentrations of refractory elements can lead to the formation of topologically-close packed (TCP) phases during exposure to conditions of high temperature and stress which result in the degradation of the creep properties. The traditional methods for predicting the occurrence of TCP phases in Ni-based superalloys have been based on the PHACOMP and newPHACOMP methodologies which are well-known to fail with respect to new generations of alloys. In this work a novel two-dimensional structure map (Nbar, deltaV/V) for TCP phases where Nbar is the valence-electron count and deltaV/V is a compositional dependent size factor. This map is found to separate the experimental data on the TCP phases of binary, ternary and multi-component TCP phases into well-defined regions corresponding to different structure types such as A15, sigma, chi, delta, P, R, mu, and Laves. In particular, increasing size factor separates the A15, sigma and chi phases from the delta, P, R, mu phases. The structure map is then also used in conjunction with CALPHAD computations of sigma phase stability to show that the predictive power of newPHACOMP for the seven component Ni–Co–Cr–Ta–W–Re–Al system is indeed poor. In order to gain a microscopic understanding of the observed structural trends, namely the differences between the two groups of TCP structures with increasing deltaV/V and the trend from A15 to sigma to chi with increasing Nbar, the electronic structure is coarse-grained from density functional theory (DFT) to tight-binding to bond-order potentials (BOPs). First, DFT is used to calculate the structural energy differences across the elemental 4d and 5d transition metal series and the heats of formation of the binary alloys Mo-Re, Mo-Ru, Nb-Re, and Nb-Ru. These calculations show that the valence electron concentration stabilizes A15, sigma and chi but destablizes mu and Laves phases. The latter are shown to be stabilized instead by relative size difference. Second, a simple canonical TB model and in combination with the structural energy difference theorem is found to qualitatively reproduce the energy differences predicted by the elemental DFT calculations. The structural energy difference theorem rationalizes the importance of the size factor for the stability of the mu and Laves binary phases as observed in the structure map and DFT heats of formation. Finally, analytic BOP theory, is employed to identify the structural origins of the energetic differences between TCP structure-types that lead to the trends found within the two-dimensional structure map.
24

Computational modelling of structure and dynamics in lightweight hydrides

Aeberhard, Philippe C. January 2012 (has links)
Hydrogen storage in lightweight hydrides continues to attract significant interest as the lack of a safe and efficient storage of hydrogen remains the major technological barrier to the widespread use of hydrogen as a fuel. The metal borohydrides Ca(BH₄)₂ and LiBH₄ form the subject of this thesis; three aspects of considerable academic interest were investigated by density functional theory (DFT) and molecular dynamics (MD) modelling. (i) High-pressure crystal structures of Ca(BH₄)₂ were predicted from a structural analogy between metal borohydrides and isoelectronic metal oxides. The structural stability of hydrogen storage materials under high pressure is an important aspect, as high-pressure polymorphs may provide structures with better hydrogen desorption properties. The isoelectronic analogue of Ca(BH₄)₂ is TiO₂, and structural equivalents of Ca(BH₄)₂ in the baddeleyite, columbite and cotunnite structures of TiO₂ were found to be stable at elevated pressure. Thermodynamic stability was evaluated by computing the Gibbs energy with respect to pressure and temperature. The pressure-dependence of the Helmholtz energy was determined to described a third-order Birch-Murnaghan equation of state, and the harmonic approximation was used to compute the vibrational energy levels and the Helmholtz energy as a function of temperature. The proposed structures are consistent with reports of two hitherto unidentified high-pressure phases observed experimentally. (ii) The disordered structure of the high-temperature phase of LiBH4 was studied by ab initio molecular dynamics (MD) at temperatures ranging from 200-535 K. It was found that the model emerging from analysis of the MD simulations properly accounts for dynamical disorder and fundamentally differs from the published experimental and theoretical structures. The validity of the MD model was corroborated by comparison of calculated pair distribution functions, vibrational spectra and a crystallographic model with neutron diffraction data; good agreement was found. A reassignment of the space group from P63mc to P63/mmc is proposed based on evidence for additional symmetry from MD simulations. (iii) Finally, a new MD-based method was developed to simulate fast ionic diffusion in LiBH₄. The colour diffusion algorithm - a nonequilibrium molecular dynamics method originally developed for the study of model fluids - was adapted and applied to self-diffusion of atoms in a solid for the first time. Calculated diffusion coefficients agreed very well with published measurements, and diffusion pathways that include collective particle effects were determined directly from the simulation results, thereby opening up a promising and efficient new method for the study of phenomena such as superionic conduction.
25

Conformational control by intramolecular hydrogen bonding

Luccarelli, James Walter January 2013 (has links)
Hydrogen bonds are directional, non-covalent interactions between hydrogen and electronegative atoms. Although generally weak, these interactions are critical to the stability of many biological systems including proteins and DNA. This dissertation explores small molecules in which an intramolecular hydrogen bond is the key determinant of conformation. Chapter 1 introduces the protein Grb2 SH3C, details its role in cancer signalling, and delineates the idea of peptidomimetics—small molecules which are functionalized to mimic the structure of a peptide and disrupt protein-protein interactions. Chapter 2 describes a virtual screen for binders to Grb2 SH3C. From a library of 6.3 million compounds, 34 were tested in vitro and two found to bind to the protein in two orthogonal assays. Chapter 3 describes mimics of the polyproline II helix using a benzoylurea scaffold. A small library of these compounds was synthesized and tested for binding to Grb2 SH3C using SPR, a competition assay, and NMR. Chapter 4 describes attempts to mimic a 310 helix using benzamide-based peptidomimetics. The synthesis and in vitro evaluation of these molecules as ligands of Grb2 SH3C is described. Chapter 5 uses quantum chemical calculations to assess the energies of a series of molecular switches. These calculations benchmark a range of modern density functional theory calculations, and attempt to quantify the accuracy of these methods for a large, flexible system. The role of solvation, entropy, geometry, and torsional angles are assessed in accurately calculating the energies of the critical hydrogen bonds.
26

Tailoring the magnetic anisotropy in amorphous FeZr-based thin films on flexible and solid substrates

Menniti, Matteo January 2018 (has links)
In this thesis the magnetic properties of novel amorphous magnetic materials grown on a flexible substrate of polyethylene naphthalate and a silicon wafer have been analyzed and characterized. The analyzed films are two films of amorphous Cobalt-Iron-Zirconium(Co36Fe53Zr11 & Co37Fe55Zr8) grown on the flexible substrate and two films of amorphous (Fe89Zr11) doped with boron (B). The B is implanted in a lattice of rings with inner diameter of 10 μm and outer diameter of 20 μm and with the distance between the center of the rings of either 50 μm or 25 μm. The composition in the doped region is Fe80Zr10B10. Various magneto-optical Kerr effect(MOKE) magnetometers are used to measure hysteresis loops of the samples and a superconducting quantum interference device (SQUID) is used to find the volume magnetization of the flexible samples. To measure the anisotropy in the flexible films a series of sample holders has been developed to measure various amount of stress using the same sample in magneto-optical magnetometers. The stress induced uniaxial anisotropy is found by measuring hysteresis loops of the flexible samples while bending them with different curvatures. The induced anisotropy is related to the magnetostriction and the magnetostriction constants is estimated for the two flexible samples by assuming values for Young’s modulus and Poisson’s ratio. The estimated values for the magnetostriction constant are found to vary with the amount of Zr and to be in the correct order of magnitude for magnetic films. The implanted B rings with the short distance of 25 μm between the center showed to have some interaction between the rings. This conclusion is drawn after analyzing first order reversal curves of the samples and looking at the domains under a MOKE-microscope. At very low temperatures the (unimplanted) FeZr matrix is ferromagnetic and seem to have an anti-ferromagnetic coupling with the B rings. At room temperature the rings are still ferromagnetic and they couple to each other.
27

Building a design system for a startup : A case study exploring how an open-source component library can assist a start-up in the creation of a design system

Häger, Erik January 2021 (has links)
The purpose of this thesis is to develop a deeper understanding of the potential benefits of using an open-source library when building a design system. The thesis uses a research through design approach in three steps; (1) identifying what a design system contains and the possible advantages of using one. (2) Building a design system based on an open-source library. (3) Evaluate how the new design system performs by comparing its performance to the possible advantages identified in step (1). In the result chapter, the design system is presented, and the design is motivated based on the brand identity. The discussion evaluates what pros and cons it might bring to use an open-source design system compared to the general advantages of design systems mentioned in the literature. It also evaluates the process and provides knowledge for anyone wanting to use an open-source design system. In the conclusion, this thesis argues that itis useful and time-saving for any company to use an open-source library when it comes to simpleand often recurring components. However, since every application solves specific problems, the creation of unique components is inevitable. Using already designed components could also limit the ideation process since the designer already have a toolkit to use when solving problems.
28

Mobilní aplikace pro správu a rezervace sportovních lekcí / Mobile App for Management and Reservation of Sports Lessons

Hynek, Tomáš January 2019 (has links)
The goal of this thesis is to create a mobile application for Android that will offer management for reservations of training lessons. There are two user roles in the application. The first one is coach who can offer his lessons to other users. Users then can book this lesson right from the application. Coach can also manage all of his lessons and see his reservations in calendar. The second type of user is an athlete who can search for training lessons by name or place distance and then he can book them. The name of the application is Fittyy and it complies with Material Design rules. It uses advanced technologies like Android Jetpack to store local data, implement MVVM model or process server requests in the background. Communication between coach and athlete was implemented using CMS system made by Dactyl Group s.r.o.
29

Aplikace pro inteligentní logování polohy z GPS pro zařízení s OS Android / Application for smart logging of the GPS position for Android OS device

Šťastný, Petr January 2016 (has links)
The goal of this thesis is create standalone service whitch should look for location, save history of locations and send actual location of user using Android OS device. Location should be send on-line. Saving is made by KML file witch this aplication generates.
30

Aplikace pro přípravu zkoušek / Application for Exam Preparation

Líbal, Tomáš January 2021 (has links)
This thesis deals with the issue of preparation of final exams at the Faculty of Information Technology of Brno University of Technology. It describes the process of design and implementation of a web application that allows teachers to create and manage room schemes and terms of individual exams. An important part of the application is also the automatic placement of students in the rooms and the generation of individual exam assignments for printing based on the given template and the method of placement. The application provides students with a clear view of individual exam terms and details about them. The work will result in a functional and usable web application written in Java using the Spring and Angular frameworks.

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