Magnetic field-assisted freeze-casting was used to create porous B4C ceramic preforms. An optimum slurry consisted of a mixture of B4C powders with 6 wt.% Er2O3 powder in an H2O-PVA solution and was cooled at a rate of 1 °C/min from room temperature to -30 °C resulting in porous green state ceramic preform with vertical channels. The Er2O3 powder was added to improve the magnetic response of the slurry. The preform was then sublimated to remove H2O and then sintered. The sintered ceramic preform was then infiltrated in the most vertically aligned channel direction with molten Al (A356) metal through a vacuum-assisted pump to create the metal matrix composite (MMC). Finite element analysis simulations were used to analyze and predict the anisotropic effect of B4C channel alignment on mechanical properties. The mechanical properties of the composite were then experimentally found via compression testing, which was compared with rule-of-mixtures and finite element modeling simulations, to analyze the effect of anisotropy due to magnetic field-assisted freeze-casting. This study reinforces the viability of cost-effective magnetic field-assisted freeze-casting as a method to create highly directional ceramic preforms, which can be subsequently metal infiltrated to produce MMCs with highly anisotropic toughness.

Although the concept of tensegrity structures was invented in the beginning of the twentieth century, the applications of these structures are limited, partially due to their low stiffness. The stiffness of tensegrities comes from topology, configuration, pre-stress and initial axial element stiffnesses.  The first part of the present work is concerned with finding the magnitude of pre-stress. Its role in stiffness of tensegrity structures is to postpone the slackening of cables. A high pre-stress could result in instability of the structure due to buckling and yielding of compressive and tension elements, respectively. Tensegrity structures are subjected to various external loads such as self-weight, wind or snow loads which in turn could act in different directions and be of different magnitudes. Flexibility analysis is used to find the critical load combinations. The magnitude of pre-stress, in order to sustain large external loads, is obtained through flexibility figures, and flexibility ellipsoids are employed to ensure enough stiffness of the structure when disturbances are applied to a loaded structure.  It has been seen that the most flexible direction is very much sensitive to the pre-stress magnitude and neither analytical methods nor flexibility ellipsoids are able to find the most flexible directions. The flexibility figures from a non-linear analysis are here utilized to find the weak directions.  In the second part of the present work, a strategy is developed to compare tensegrity booms of triangular prism and Snelson types with a truss boom. It is found that tensegrity structures are less stiff than a truss boom when a transversal load is applied. An optimization approach is employed to find the placement of the actuators and their minimum length variations. The results show that the bending stiffness can be significantly improved, but still an active tensegrity boom is less stiff than a truss boom. Genetic algorithm shows high accuracy of searching non-structural space. / QC 20110524

Performing optimization of structures is always of great interest. There are several different ways to optimize steel structures. Today, several companies are having difficulties with their cable drums during transport. Cable drums with full cable load become heavy and make it difficult to transport. This paper aims to examine existing published research and approaches, with a focus on steel optimization. This paper has two research objectives, the first one is to examine the possibilities for optimizing cable drums in terms of mass without compromising load capacity or yield stress. The second question is to determine how much of the weight/mass of cable drums may be reduced via optimization. To optimize it, measurements, cable drum modeling, research studies, and connecting suitable software's will be carried out in this paper. Participation Action Research and Reverse Engineering methodologies were implemented in combination. A literature review was performed to get a deeper understanding of the methods. A systematic literature review was done to identify available approaches and techniques for structural steel optimization. In order to optimize the cable drum, Excel and Autodesk Inventor were connected through Visual Basic Applications (VBA). The optimization process workflow acted with a server and two clients, where Excel acted as the server and Autodesk Inventor and MATLAB acted as clients. It was found that this was a suitable method for optimizing the cable drum were to work with an optimization process that included connecting a server with clients. The MATLAB function fmincon was applied with both interior-point algorithm and Sequential Quadratic Programming (SQP). The optimal design variables for the cable drum were established, and the objective minimization was accomplished by reducing the cable drum mass of 2495.20 kg. The cable drums mass was minimized to 101.86 kg. The literature review was systematically conducted to find available approaches and methods for structural steel optimization. The combination of Participatory Action Research (PAR) and Reverse Engineering (RE) was ideal for this project since it enabled both approaches to gather data on cable drum capacity and alternative optimization strategies.The schematic optimization workflow was appropriate to apply throughout the implementation phase. The workflow gave the user complete control over the optimization process, and the automated process saved time and was simple to adapt.

<p>NR 20140805</p>

During construction of dams, rock bolts are in general installed in the interface between concrete and rock as an extra safety measure against overturning failure. These bolts are however not allowed to be taken into consideration for the stability calculations of large dams. New standards and new design criterias have increased the requirements of the safety of the old dams, leading to a need for expensive rehabilitation and strengthening. It is possible that consideration of these bolts in stability calculations may lead to money being saved. In order to do so more information about the long term strength of these bolts is needed. One way of getting this information has been the destructive testing of old dugout bolts found during reconstruction works. At the Lima hydropower station in Sweden, this kind of testing was made. The test rig used had a design where a piston pressed down on the rock around the bolt in order to pull it out. The question was raised if this could affect the failure load of the bolt. In this thesis, an attempt was made to answer this question using finite element methods. Models of a rock bolt was made in Abaqus, where one model included the piston and one where it was not. The connection between the bolt and the rock was modelled with nonlinear springs and friction, and the results were then compared between the cases and with experimental data. The results showed that the resulting force-deformation curves may be affected by the piston in cases where the dominant failure mode was adhesive failure, which would influence failure loads and deformations. Since so little was known about the properties of the rock and grout at Lima however, it is difficult to say to which extent the test rig has affected these results.

A spacecraft is subjected to dynamic and static loads during launch. These loads are deterministic and of random nature and cannot be tested under the real conditions due to cost considerations. The spacecraft must therefore sustain certain mechanical loads without permanent deformation with a certain safety factor due to the uncertainties in the actual loading values during launch. The applicable mechanical test requirements and load combination have been first determined for the structure of interest: the SEAM CubeSat. These requirements are found to be steady-state accelerations, random vibration and shock response spectrum loadings. They have been simulated onto the structure globally and locally in order to extract stress values, amend design features when necessary and determine adequate material properties in order for the final design to fulfill the mechanical requirements during launch. / En satellit utsätts för dynamiska och statiska belastningar under uppskjutningen. Dessa laster är av deterministisk och av slumpmässig natur och kan inte testas under verkliga förhållanden på grund av kostnadsskäl. Satellitens konstruktion måste därför klara att utsättas för utan permanent deformation med en viss säkerhetsfaktor på grund av osäkerheter i de faktiska belastningarna under uppskjutningen. Mekaniska provningskrav och lastkombinationer har bestämts för en utvald struktur: SEAM CubeSat. Dessa krav visar sig vara accelerationer, slumpmässiga vibrationer och stötar. Strukturen har simulerats globalt och lokalt för att få fram de mekaniska belastningarna. Baserat på resultat från simuleringarna har konstruktionen modifierats och lämpliga material egenskaper har bestämts för att den slutliga konstruktionen ska uppfylla de mekaniska kraven under uppskjutningen.

The aim of this thesis is to analyse the effects of train induced vibrations in a steel Langer beam bridge. A case study of a bridge over the river Ljungan in Ånge has been made by analysing measurements and comparing the results with a finite element model in ABAQUS. The critical details of the bridge are the hangers that are connected to the arches and the main beams. A stabilising system has been made in order to reduce the vibrations which would lead to increased life length of the bridge. Initially, the background to this thesis and a description of the studied bridge are presented. An introduction of the theories that has been applied is given and a description of the modelling procedure in ABAQUS is presented. The performed measurements investigated the induced strain and accelerations in the hangers. The natural frequency, the corresponding damping coefficients and the displacement these vibrations leads to has been evaluated. The vibration-induced stresses, which could lead to fatigue, have been evaluated. The measurement was made after the existing stabilising system has been dismantled and this results in that the risk of fatigue is excessive. The results were separated into two parts: train passage and free vibrations. This shows that the free vibrations contribute more and longer life expectancy could be achieved by introducing dampers, to reduce the amplitude of the amplitude of free vibrations. The finite element modelling is divided into four categories: general static analysis, eigenvalue analysis, dynamic analysis and detailed analysis of the turn buckle in the hangers. The deflection of the bridge and the initial stresses due to gravity load were evaluated in the static analysis. The eigenfrequencies were extracted in an eigenvalue analysis, both concerning eigenfrequencies in the hangers as well as global modes of the bridge. The main part of the finite element modelling involves the dynamic simulation of the train passing the bridge. The model shows that the longer hangers vibrate excessively during the train passage because of resonance. An analysis of a model with a stabilising system shows that the vibrations are damped in the direction along the bridge but are instead increased in the perpendicular direction. The results from the model agree with the measured data when dealing with stresses. When comparing the results concerning the displacement of the hangers, accurate filtering must be applied to obtain similar results.

Multiple studies on the microstructures of advanced high-strength steels are presented here that seek to add to the already substantial body of knowledge on martensite in steel. These studies seek to gain additional insight into the role that the martensite transformation has on the observed mechanical properties of modern steels. Crystallographic Reconstruction of Parent Austenite Twin Boundaries in a Lath Martensitic Steel The study of post-transformation microstructures and their properties can be greatly enhanced by studying their dependence on the grain boundary content of parent microstructures. Recent work has extended the crystallographic reconstruction of parent austenite in steels to include the reconstruction of special boundaries, such as annealing twins. These reconstructions present unique challenges, as twinned austenite grains share a subset of possible daughter variant orientations. This gives rise to regions of ambiguity in a reconstruction. A technique for the reconstruction of twin boundaries is presented here that is capable of reconstructing 60 degree twins, even in the case where twin regions are comprised entirely of variants that are common between the twin and the parent. This technique is demonstrated in the reconstruction of lath martensitic steels. The reconstruction method utilizes a delayed decision-making approach, where a chosen orientation relationship is used to define all possible groupings of daughter grains into possible parents before divisive decisions are made. These overlapping, inclusive groupings (called clusters) are compared to each other individually using their calculated parent austenite orientations and the topographical nature of the overlapping region. These comparisons are used to uncover possible locations of twin boundaries present in the parent austenite. This technique can be applied to future studies on the dependence of post-transformation microstructures on the special grain boundary content of parent microstructures. Coupling Kinetic Monte Carlo and Implicit Finite Element Methods for Predicting the Strain Path Sensitivity of the Mechanically Induced Martensite Transformation The kinetic Monte Carlo method is coupled with a finite-element solver to simulate the nucleation of martensite inside the retained austenite regions of a TRIP (transformation induced plasticity) assisted steel. Nucleation kinetics are expressed as a function of load path and kinematic coupling between retained austenite regions. The model for martensite nucleation incorporates known elements of the kinetics and crystallography of martensite. The dependence of martensite transformation on load path is simulated and compared to published experimental results. The differences in transformation rates of retained austenite are shown to depend on load path through the Magee effect. The effects of average nearest neighbor distance between austenite grains is shown to affect the rate at which martensite nucleates differently depending on load path. Ductility and Strain Localization of Advanced High-Strength Steel in the Presence of a Sheared Edge The localization of strain in the microstructures of DP 980 and TBF 980 is quantified and compared. Of particular interest is the difference in final elongation observed for both materials in the presence of a sheared edge. Scanning electron micrographs of etched microstructures near the sheared edge are gathered for both materials at varying amounts of macroscopic strain. These micrographs are used to generate strain maps using digital image correlation. A two point statistical measure for strain localization is developed that utilizes strain map data to quantify the degree to which strain localizes around the hard phase of both materials. The DP steel exhibits higher strain localization around the martensite phase. Reasons for differences in strain localization and shear banding between the two materials are suggested, and the role played by the mechanically induced martensite transformation is speculated.

In recent decades, railway transport infrastructures have been regaining their importance due to their efficiency and environmentally friendly technologies. This has led to increasing train speeds, higher axle loads and more frequent train usage. These improved service provisions have however brought new challenges to traditional railway track engineering, especially to track geotechnical dynamics. These challenges demanded for a better understanding of the track dynamics. Due to the large cost and available load conditions limitation, experimental investigation is not always the best choice for the dynamic effect study of railway track structure. Comparatively speaking, an accurate mathematical modeling and numerical solution of the dynamic interaction of the track structural components reveals distinct advantage for understanding the response behavior of the track structure. The purpose of this thesis is to study the influence of design parameters on dynamic response of the railway track structure by implementing Finite Element Method (FEM). According to the complexity, different railway track systems have been simulated, including: Beam on discrete support model, Discretely support track including ballast mass model and Rail on sleeper on continuum model. The rail and sleeper have been modeled by Euler-Bernoulli beam element. Spring and dashpot has been used for the simulation of railpads and the connection between the sleeper and ballast ground. Track components have been studied separately and comparisons have been made between different models. The finite element analysis is divided into three categories: eigenvalue analysis, dynamic analysis and general static analysis. The eigenfrequencies and corresponding vibration modes were extracted from all the models. The main part of the finite element modeling involves the steady-state dynamic analysis, in which receptance functions were obtained and used as the criterion for evaluating the dynamic properties of track components. Dynamic explicit analysis has been used for the simulation of a moving load, and the train speed effect has been studied. The displacement of the trackbed has been evaluated and compared to the measurement taken in Sweden in the static analysis.

To deal with an increasing demand in transportation, trains are made longer and faster. Higher speeds imply higher impacts on bridges. Therefore, structures have to be designed to resist these new constraints. The Eurocode (2002) introduced additional checks for the design of high-speed railway bridges. Among them, the maximum vertical deck acceleration criterion often determines alone the design of the structure. Tests on shake table brought to the conclusion that vertical bridge deck acceleration should never exceed 3.5 m/s2 for ballasted tracks. This master thesis investigates the optimization of cross section parameters of single-track simply supported and double-span bridges based on the limit of the maximum vertical deck acceleration criterion. The first natural frequency is considered as a proof of the feasibility of the structure. The optimization is carried out through MATLAB for both types of bridges. The deck acceleration of simply supported bridges is analytically calculated using the Train Signature (ERRI D214 1999) in MATLAB. The dynamic calculations of double-span bridges are implemented through the finite element software ABAQUS. The implemented programs have been verified by comparison to values of simple cases found in the literature. Structures are tested under the influence of the ten HSLM-A trains of the Eurocode running at speeds between 150 km/h and 350 km/h. Optimization algorithms are presented and compared in this study but their applicability in such context is questioned. Indeed, as the problem contains several suitable minima, the algorithms, which end in one solution, are not adapted. To overtake this difficulty, a scanning of the interesting zone is advised. However, the latter is very time consuming, even more if the finite element analysis is used. Suggestions to decrease analysis time are presented in this report. Single span composite bridges with a span longer than 20 m appeared to be impossible to optimize within the objectives defined in this work (i.e. considering limits of deck acceleration and first natural frequency), which draws doubts about their suitability for high-speed railways. Nevertheless, simply supported bridges made of concrete seem more adapted for high-speed railways and their optimized parameters are presented in this work. Optimized parameters for double-span concrete bridges are also presented.