Introduction: Zygomatic fractures form a major entity in craniomaxillofacial traumatology. Few studies have dealt with biomechanical basics and none with the role of the facial soft tissues. Therefore this study should investigate, whether facial soft tissue plays a protecting role in lateral midfacial trauma.

Total Hip Arthroplasty (THA) is an orthopaedic procedure that is performed to reduce pain and restore the functionality of hip joints that are affected by degenerative diseases. The outcomes of THA are generally good. However, the stress shielding of the periprosthetic femur is a factor that can contribute towards the premature loosening of the femoral stem. In order to improve the stress shielding characteristics of metallic femoral stems, stiffness configurations that offer more flexibility should be considered. This research has investigated the potential of more flexible and lightweight cobalt chromium molybdenum (CoCrMo) femoral stems that can be manufactured using Selective Laser Melting (SLM). Square pore cellular structures with compressive properties that are similar to human bone have been presented and incorporated into femoral stems by utilising fully porous and functionally graded designs. A three dimensional finite element model has been developed to investigate and compare the load transfer to the periprosthetic femur when implanted with femoral stems offering different stiffness configurations. It was shown that the load transfer was improved when the properties of the square pore cellular structures were incorporated into the femoral stem designs. Factors affecting the manufacturability and production of laser melted femoral stems have been investigated. A femoral stem design has been proposed for cemented or cementless fixation. Physical testing has shown that a functionally graded stem can be repeatedly manufactured using SLM, which was 48% lighter and 60% more flexible than a traditional CoCrMo prosthesis. The research presented in this thesis has provided an early indication of utilising SLM to manufacture lightweight CoCrMo femoral stems with levels of flexibility that have the potential to reduce stress shielding in the periprosthetic femur.

Intensive competition on the global market puts great pressure on manufacturing companies to develop and produce products that meet requirements from customers and investors. One key factor in meeting these requirements is the efficiency of the product development and the production preparation process. Design automation is a powerful tool to increase efficiency in these two processes. The benefits of automating the production preparation process are shortened led-time, improved product performance, and ultimately decreased cost. Further, automation is beneficial as it increases the ability to adapt products to new product specifications with production preparations done in few or in a single step. During the automation process, knowledge about the production preparation process is collected and stored in central systems, thus allowing full control over the design of production equipments. Three main topics are addressed in this thesis: the flexibility of design automation systems, knowledge bases containing conflicting rules, and the automation of the finite element analysis process. These three topics are discussed in connection with the production preparation process of rotary draw bending. One conclusion drawn from the research is that it is possible to apply the concept of design automation to the production preparation process at different levels of automation depending on characteristics of the implemented knowledge. In order to make design automation systems as flexible as possible, the concept of object orientation should be adapted when building the knowledge base and when building the products geometrical representations. It is possible to automate the process of setting up, running, and interpreting finite element analyses to a great extent and making the automated finite element analysis process a part of the global design automation system.

Assessing long-term rock stability is an important aspect in the analysis of slopes, dam and bridge foundations, and other infrastructure. Rock behavior over tens to thousands of years must be anticipated when predicting the performance of, for example, an underground containment facility for nuclear waste. At such long time scales, the time dependence of rock failure, typically ignored in short time scale analyses, has a significant effect and must be included in the analysis. Since time-dependent rock behavior is thought to be caused by the subcritical growth of microcracks, a time-dependent analysis should incorporate a method of simulating subcritical crack growth. In this thesis, a rock bridge damage model was developed using the finite element program Abaqus to simulate subcritical crack growth for all three modes of crack tip displacement in three-dimensional rock masses. Since subcritical crack growth is not among the damage initiation and evolution criteria available in Abaqus, its effect was included in the model through the USDFLD user subroutine. Material properties for the damage model were obtained through laboratory fracture toughness testing of Escabrosa limestone from Kartchner Caverns. Tests included the grooved disk test for mode I, the punch-through shear with confining pressure test for mode II, and the circumferentially-notched cylindrical specimen test for mode III. The subcritical crack growth parameters n and A were calculated for all three modes using the constant stress-rate method. Fracture test results were compared with a previous study by Tae Young Ko at the University of Arizona, which tested Coconino sandstone and determined that the subcritical crack growth parameters were consistent among modes. This thesis expands upon Ko's work by adding the characterization of a second rock material in all three modes; results indicate that for Escabrosa limestone the subcritical crack growth parameters are not consistent among modes. Additionally, the Escabrosa limestone composing the caverns ranges from a more homogeneous, even-grained texture to a more heterogeneous texture consisting of coarse-grained veins and solution cavities set in a fine-grained matrix. To determine if the veined regions are more susceptible to fracturing and act as the nuclei of rock bridge failure, the fracture toughness tests were conducted separately for each texture. Results indicate that the more heterogeneous limestone has a higher fracture strength, fracture toughness, and subcritical crack growth index n than the more homogeneous limestone. This is in agreement with previous studies that determined that a more complex and heterogeneous microstructure produces a larger microcrack process zone and a more tortuous crack path, leading to higher fracture energies and larger values of n. Application of the rock bridge damage model to a simplified Kartchner cave room with a single roof block provided visualization of decreasing rock bridge size and produced time-to-failure estimates of 1,251 to 65,850 years. Multiple models were run to study the effect of (i) using material properties from each of the two textures identified in the Escabrosa limestone and (ii) varying the in-situ stress ratio, K. Both the value of K and the choice of Escabrosa texture had a large effect on the estimated time-to-failure, indicating that for future modeling of Kartchner accurate estimation of the in-situ stress ratio is as important as field identification of homogeneous vs. heterogeneous textures.

This research aims at understanding the conditions that lead to reaction initiation of polymer-bonded explosives (PBXs) as they undergo mechanical and thermal processes subsequent to impact. To analyze this issue, a cohesive finite element method (CFEM) based finite deformation framework is developed and used to quantify the thermomechanical response of PBXs at the microstructure level. This framework incorporates the effects of large deformation, thermomechanical coupling, failure in the forms of micro-cracks in both bulk constituents and along grain/matrix interfaces, and frictional heating. A novel criterion for the ignition of heterogeneous energetic materials under impact loading is developed, which is used to quantify the critical impact velocity, critical time to ignition, and critical input work at ignition for non-shock conditions as functions of microstructure of granular HMX and PBX. A threshold relation between impact velocity and critical input energy at ignition for non-shock loading is developed, involving an energy cutoff and permitting the effects of microstructure and loading to be accounted for. Finally, a novel approach for computationally predicting and quantifying the stochasticity of the ignition process in energetic materials is developed, allowing prediction of the critical time to ignition and the critical impact velocity below which no ignition occurs based on basic material properties and microstructure attributes. Results are cast in the form of the Weibull distribution and used to establish microstructure-ignition behavior relations.

This thesis describes the optimization process for the pitchfork developed by the company Sverigegrepen. The work was done at the department of Applied Mechanics at Uppsala University. The project were handed by Ångström Materials Academy together with Sverigegrepen The work included a major prestudy of plastic construction, plastic materials, plastic injection and strength of materials. By applying the laws of beam theory, a mathematical expression could be provided, explaining the behaviour of the pitchforks teeth. By studying the pitchfork with tools such as 3D- CAD and FEA-simulations, an area where high concentrations of stress were found, an area known to have frequent issues with strength. From this data several concepts were created with an increased strength and a better distribution of stress. The plastic material was evaluated and tested to find the most valuable material characteristics. The provided information was used to isolate different functions in plastic materials, which is crucial for the pitchforks further functionality.

Carbon fabric-reinforced polymer (CFRP) composites are widely used in aerospace, automotive and construction structures thanks to their high specific strength and stiffness. They can also be used in various products in sports industry. Such products can be exposed to different in-service conditions such as large bending deformations caused by quasi-static and dynamic loading. Composite materials subjected to such bending loads can demonstrate various damage modes - matrix cracking, delamination and, ultimately, fabric fracture. Damage evolution in composites affects both their in-service properties and performance that can deteriorate with time. Such damage modes need adequate means of analysis and investigation, the major approaches being experimental characterisation and numerical simulations. This work deals with a deformation behaviour and damage in carbon fabric-reinforced polymer (CFRP) laminates caused by quasi-static and dynamic bending. Experimental tests are carried out first to characterise the behaviour of a CFRP material under tension, in-plane shear and large-deflection bending in quasi-static conditions. The dynamic behaviour of these materials under large-deflection bending is characterised by Izod-type impact tests employing a pendulum-type impactor. A series of impact tests is performed on the material at various impact energy levels up to its fracture, to obtain a transient response of the woven CFRP laminate. Microstructural examination of damage is carried out by optical microscopy and X-ray micro computed tomography (Micro-CT). The damage analysis revealed that through thickness matrix cracking, inter-ply delaminations, intra-ply delamination such as tow debonding, and fabric fracture was the prominent damage modes. These mechanical tests and microstructural studies are accompanied by advanced numerical models developed in a commercial code Abaqus. Among those models are (i) 2D FE models to simulate experimentally observed inter-ply delamination, intra-ply fabric fracture and their subsequent interaction under quasi-static bending conditions and (ii) 3D FE models based on multi-body dynamics used to analyse interacting damage mechanisms in CFRP under large-deflection dynamic bending conditions. In these models, multiple layers of bilinear cohesive-zone elements are placed at the damage locations identified in the Micro CT study. Initiation and progression of inter-laminar delamination and intra-laminar ply fracture are studied by employing cohesive elements. Stress-based criteria are used for damage initiation while fracture-mechanics techniques are employed to capture its progression in composite laminates. The developed numerical models are capable to simulate the studied damage mechanisms as well as their subsequent interaction observed in the tests and microstructural damage analysis. In this study, a novel damage modelling technique based on the cohesive-zone method is proposed for analysis of interaction of various damage modes, which is more efficient than the continuum damage mechanics approach for coupling between failure modes. It was observed that the damage formation in the specimens was from the front to the back at the impact location in the large-deflection impact tests, unlike the back-to-front one in drop-weight tests. The obtained results of simulations showed a good agreement with experimental data, thus demonstrating that the proposed methodology can be used for simulations of discrete damage mechanisms and their interaction during the ultimate fracture of composites in bending. The main outcome of this thesis is a comprehensive experimental and numerical analysis of the deformation and fracture behaviours of CFRP composites under large-deflection bending caused by quasi-static and dynamic loadings. Recommendations on further research developments are also suggested.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Several transverse flux and longitudinal flux linear generator topologies exist for freepiston Stirling engine applications. In this thesis the transverse flux permanent magnet linear generators are investigated together with a back-to-back converter which can deliver the electrical energy from the linear generator to the electrical network. The transverse flux permanent magnet linear generator is geometrically optimised with the aim to maximise the power-to-weight ratio while maintaining preset power and efficiency levels. An optimised 3 kW linear generator is built and the measured results correlate to the simulation results. A close-loop current control scheme is introduced to control the current of the rectifier, which is part of the back to back converter. The transverse flux permanent magnet linear generator is connected to the input of the rectifier which has the ability to force a specific current from the generator. The measured results of the rectifier correlate to the results of the simulations that were done. The current control present some complications and it is suggested that another control scheme is used. A close-loop voltage control scheme is introduced for the control of the DC bus voltage. The DC bus is connected between the rectifier and the inverter, which is the other part of the back-to-back converter. A close-loop current control scheme is introduced to control the inverter current that flows from the inverter to the electrical network. The measured results of the inverter and the DC bus correlate to the results of the simulations that were done. The results of the system, including the generator, rectifier and inverter, tested as a unit is presented and discussed. / AFRIKAANSE OPSOMMING: Verskeie tranverse vloed en longitudinale vloed lineˆere generator topologie¨e bestaan vir vrysuier Stirling enjin toepassings. In hierdie tesis word ’n transverse vloed permanente magneet lineˆere generator ondersoek saam met ’n omsetter. Die omsetter dra die elektriese energie van die generator oor aan die elektriese netwerk. Die transverse vloed permanente magneet lineˆere generator word geometries geoptimeer met die doel om die drywing-tot-gewig verhouding te maksimiseer terwyl vasgestelde drywing en effektiwiteit vlakke behou word. ’n Geoptimeerde 3kW lineˆere generator prototipe is vervaardig en die gemete resultate is geverifieer met die simulasie resultate. ’n Geslote lus stroombeheer strategie word voorgestel om die stroom te beheer van die gelykrigter, wat deel is van die omsetter. Die transverse vloed permanente magneet lineˆere generator word aan die gelykrigter, wat die vermo¨e het om ’n spesifieke stroom uit die generator te forseer, se intree verbind. Die gemete resultate van die gelykrigter wat gebou is stem goed ooreen met die van die simulasies wat gedoen is. Die stroombeheer hou komplikasies in wat bespreek word. Dus word die gebruik van ’n alternatiewe stroombeheer voorgestel. ’n Geslote lus spannings beheer strategie¨e word voorgestel om die gs. busspanning te beheer. Die gs. bus is gekonnekteer tussen die gelykrigter en die wisselrigter, wat ook deel uitmaak van die omsetter. ’n Geslote lus stroom beheer word voorgestel om die stroom te beheer wat vanaf die wisselrigter na die elektriese netwerk toe vloei. Die gemete resultate van die wisselrigter en die gs. bus stem goed ooreen met die van die simulasies wat gedoen is. Die resultate van die hele stelsel, wat die generator, gelykrigter en die wisselrigter insluit, wat as ’n eenheid getoets is word weergegee en bespreek.

A large structural weldment has been designed to serve as the new star tracker bridge for the Dark Energy Experiment upgrade to the Hobby-Eberly Telescope at McDonald Observatory. The modeling approach, analysis techniques and design details will be of interest to designers of large structures where stiffness is the primary design driver. The design includes detailed structural analysis using finite element models to maximize natural frequency response and limit deflections and light obscuration. Considerable fabrication challenges are overcome to allow integration of precision hardware required for positioning the corrector optics to a precision of less than 5 microns along the 4-meter travel range. This thesis provides detailed descriptions of the bridge geometry, analysis results and challenging fabrication issues. / text

Surface integrity of manufactured components has a critical impact on their functional performance. Magnesium alloys are lightweight materials used in the transportation industry and are also emerging as a potential material for biodegradable medical implants. However, the unsatisfactory corrosion performance of Mg alloys limits their application to a great extent. Surface integrity factors, such as grain size, crystallographic orientation and residual stress, have been proved to remarkably influence the functional performance of magnesium alloys, including corrosion resistance, wear resistance and fatigue life. In this dissertation, the influence of machining conditions, including dry and cryogenic cooling (liquid nitrogen was sprayed to the machined surface during machining), cutting edge radius, cutting speed and feed rate, on the surface integrity of AZ31B Mg alloy was investigated. Cryogenic machining led to the formation of a "featureless layer" on the machined surface where significant grain refinement from 12 μm to 31 nm occurred due to dynamic recrystallization (DRX), as well as increased intensity of basal plane on the surface and more compressive residual stresses. Dry and cryogenic burnishing experiments of the same material were conducted using a fixed roller setup. The thickness of the processed-influenced layer, where remarkable microstructural changes occurred, was dramatically increased from the maximum value of 20 μm during machining to 3.4 mm during burnishing. The burnishing process also produced a stronger basal texture on the surface than the machining process. Preliminary corrosion tests were conducted to evaluate the corrosion performance of selected machined and burnished AZ31B Mg samples in 5% NaCl solution and simulated body fluid (SBF). Cryogenic cooling and large edge radius tools were found to significantly improve the corrosion performance of machined samples in both solutions. The largest improvement in the material's corrosion performance was achieved by burnishing. A finite element study was conducted for machining of AZ31B Mg alloy and calibrated using the experimental data. A user subroutine was developed and incorporated to predict the grain size changes induced by machining. Good agreements between the predicted and measured grain size as well as thickness of featureless layers were achieved. Numerical studies were extended to include the influence of rake angle, feed rate and cutting speed on the featureless layer formation.