A method to study the response in materials exposed to high energy laser pulses has been developed in this thesis. The method is based on focused and defocused Speckle Correlation and uses an illumination cw laser and digital camera to acquire images of speckle patterns. These images were captured using a CCD camera before, during and after the laser drilling processing and were saved in a computer. All image processing was performed after the drilling process has been finished. By using this method the size of the affected zone, in-plane strain, surface tilt and surface deformations can be quantified with the temporal resolution limited by the frequency of the camera being used. This thesis comprises three papers. One conference paper was presented at the International Conference on Laser-Matter Interaction in St.Petersburg 2003, and two papers were submitted to Applied Optics. Results are shown from single shot interaction on sheets of Al2O3 and stainless steel as well as responses in sheets of copper and silver during percussion hole drilling. The results obtained during processing are also compared with SEM images. It is concluded that the method gives valuable information about the drilling process and that it is a robust and highly sensitive alternative to Interferometry for the study of laser-matter interaction processes. / Godkänd; 2004; 20070128 (ysko)

The welding process introduces residual stress originating from the heating, melting and cooling of the material. From the point of view of fatigue and stress corrosion cracking, the weld residual stress perpendicular to the weld axis is of particular interest. When qualifying weld parameters for welds in large cylinders having a ratio of radius to plate thickness larger than say approximately 100; reference to plane plates are often made for the sake of simplicity. However, the weld residual stress perpendicular to the weld axis is severely underestimated in the plane plate compared with the cylindrical structure. This observation is especially pronounced in connection with preheating. The source of the differences is probably due to the radial constraint of the cylinder, compared with that of a plane plate. A plane test specimen will underestimate the weld residual stress perpendicular to the weld axis in a cylinder, even if the radius of the cylinder is very large. However, a test specimen for an 8 m diameter cylinder with a plate thickness of 35 mm needs only to have a segment width of approximately 1.3 m to reflect the stress in the real structure. The weld residual stress perpendicular to the weld axis in the vicinity of the weld toe is governed by the depositing of the weld bead adjacent to the weld toe, neglecting the accumulated strain from the previous deposited weld beads in the multi-pass joint weld. Introducing tensile straining perpendicular to the weld axis during the entire welding procedure reduces the weld-induced residual stress after completed welding. The plastic zone of the weld area will be subjected to compressive strain after completed welding, which in turn will reduce the weld residual stress. This can be achieved by cooling the weld area, which in this case is not recommended since the material is sensitive to hydrogen cracking, or by pre-stretching or modifying the locations for preheating, all aimed to impose a tensile axial straining around the weld area during the entire welding process. / Godkänd; 2004; 20070131 (ysko)

The ever-growing demand for renewable energy leads to an increased need for innovation in the green energy sector. One of the available alternatives, wind power, have seen a global increase in usage with few signs of slowing down. To increase the efficiency of individual turbines, correct placement is crucial. One technology that uses sound to find optimal locations for wind turbines is Sonic Detection and Ranging, SODAR. AQ system manufacture and deliver SODAR-systems internationally. The size of the system created by AQs limit the locations which the system can measure wind. Occasionally this forces measurement to be made away from the location in question which potentially reduce the efficiency of the future wind turbine. This study aims to create a concept for a smaller version of the SODAR-system manufactured by AQs. A smaller system would allow wind measurement in more remote, hard to reach locations which in turn would increase precision of the measurements and potentially efficiency of wind turbines.   Tools from Ulrich & Eppingers product development process was used to generate, screen, and evaluate concepts throughout the study. By changing the geometry and positioning of individual components in the system the height was reduced by 49,7% and width by 32,8%. An even smaller concept could be presented if more focus was put on the base of the product. Many factors that could impact the function of the product have been ignored in this study. Based on the specifications put up for this project the concept could theoretically perform as the original AQ510. Considering that relevant factors have been ignored, the function of the concept cannot be guaranteed. The tools and methods used in the product development process facilitated the development and made it possible to present a concept within the time frame. The conclusion is that, based on the specifications presented, the concept reached the goals put up for the project but to be able to guarantee the performance of the concept, measurements and tests are needed.

The main objective of the work presented in this Licentiate thesis is to investigate and model the cyclic behaviour of an additively manufactured ductile nickel-based superalloy, with special emphasis on modelling the stabilised material behaviour, which is of interest for fatigue life predictions. Cyclic fatigue tests at different temperatures have been performed to investigate the cyclic mechanical behaviour of the material, where specimens built in different orientations have been used to also study the anisotropic behaviour of the material. Based on the tests, a constitutive description has progressively been developed and implemented in a finite element context that incorporates the anisotropic behaviour under both elastic and inelastic deformations. In addition, the room temperature crack initiation behaviour has been studied and modelled. This thesis is divided into two parts. The first part gives an introduction and background to the research, while the second part consists of three included papers. / Det huvudsakliga målet med arbetet som presenteras i denna avhandling har varit att studera och modellera det cykliska beteendet hos en additivt tillverkad duktil nickelbaserad superlegering, med fokus på att modellera det stabiliserade materialbeteendet, vilket är av intresse vid livslängdprediktering. Cykliska utmattningsprov vid olika temperaturer har utförts för att studera det cykliska beteendet hos materialet, där provstavar byggda i olika riktningar har använts för att studera materialets anisotropi. Baserat på proven har en konstitutiv beskrivning av material progressivt utvecklats och implementerats i ett finita element-verktyg, där modellen tar hänsyn till det anisotropa materialbeteendet för både elastiska och plastiska deformationer. En modell för prediktering av sprickinitiering vid rumstemperatur har också tagits fram. Denna avhandling består av två delar. Den första delen ger en introduktion samt bakgrund till forskningen, medan den andra delen består av tre inkluderade artiklar. / <p>Ytterligare forskningsfinansiär: Siemens Industrial Turbomachinery AB</p>

Bone is a living material. It adapts, in an optimal sense, to loading by changing its density and trabeculae architecture - a process termed remodelling. Implanted orthopaedic devices can significantly alter the loading on the surrounding bone. In addition, these devices rely on bone ingrowth to ensure secure implant fixation. In this project, a computational model that accounts for bone remodelling is developed and used to elucidate the response of bone following a reverse shoulder procedure. The reverse shoulder procedure investigated here is for rotary cuff deficient patients. In this procedure up to 75 % complications are reported in some clinical series. It is therefore necessary, for the design of successful implants, to understand the loading environment to promote bone growth in the correct areas. The physical process of remodelling is modelled using continuum scale, open system thermodynamics whereby the density of bone evolves isotropically in response to the loading it experiences. The fully-nonlinear continuum theory is solved approximately using the finite element method. The finite element library AceGEN forms the basis for the implementation. Several benchmark problems were implemented to validate the code and demonstrate features of the theory. These include several one-dimensional problems, the classical two-dimensional femur benchmark, and a series of three-dimensional examples. The three-dimensional examples include different loading scenarios on a rectangular block, as well as the investigation of the ASTM testing procedure of the glenoid side prosthesis implanted in a polyurethane foam block. The results clearly demonstrate the adaptive behaviour of the bone density in response to the magnitude and duration of the loading. The numerical implementation is also shown to be robust. The remodelling of the scapula post reverse shoulder arthroplasty is then investigated. A statistical shape model of the scapula was obtained from collaborators in the Division of Biomedical Engineering at the University of Cape Town. The finite element model was used to determine the density distribution in the scapula prior to surgery. A virtual surgery was then performed. The resulting geometry provides the input for the pre-processing phase of the post reverse shoulder arthroplasty model. The loading conditions for the reverse shoulder were provided by collaborators in the Division of Biomedical Engineering and the Leon Root Motion Analysis Laboratory at the Hospital for Special Surgery in New York City. The maximal loading condition at 90° abduction is used as the input for the simulation. It was found that the density increases in the vicinity of the screws, where the maximum stresses are concentrated, however, bone resorption is observed directly below and adjacent to the implant. No conclusive statement can be made, however, as only one loading scenario is considered and calibration of the model against experimental results is still outstanding. A unique feature of the code is that the upper and lower bounds of the density do not have to be enforced directly, as done in most bone remodelling theories in the literature. Rather, the bounds of the density are naturally enforced by calibrating the mass flux for the problem at hand. This project lays out the groundwork for a sound remodelling code, which can serve as a predictive tool in the field of orthopaedics.

Computational cardiac mechanics has historically relied on classical continuum models; however, classical models amalgamate the behaviour of a material's micro-constituents, and thus only approximate the macroscopically observable material behaviour as a purely averaged response that originated on micro-structural levels. As such, classical models do not directly and independently address the response of the cardiac tissue (myocardium) components, such as the muscle fibres (myocytes) or the hierarchically organized cytoskeleton. Multiscale continuum models have developed over time to account for some of the micro-architecture of a material, and allow for additional degrees of freedom in the continuum over classical models. The micromorphic continuum [15] is a multiscale model that contains additional degrees of freedom which lend themselves to the description of fibres, referred to as micro-directors. The micromorphic model has great potential to replicate certain characteristics of the myocardium in more detail. Specifically, the micromorphic micro-directors can represent the myocytes, thus allowing for non-affine relative deformations of the myocytes and the extracellular matrix (ECM) of tissue constraining the myocytes, which is not directly possible with classical models. A generalized micromorphic approach of Sansour [73, 74, 75] is explored in this study. Firstly, numerical examples are investigated and several novel proofs are devised to understand the behaviour of the micromorphic model with regards to numerical instabilities, micro-director displacements, and macro-traction vector contributions. An alternative micromorphic model is developed by the author for comparison against Sansour's model regarding the handling of micro-boundary conditions and other numerical artifacts. Secondly, Sansour's model is applied to cardiac modelling, whereby a macro-scale strain measure represents the deformation of the ECM of the tissue, a micro-scale strain measure represents the muscle fibres, and a third strain measure describes of the interaction of both constituents. Separate constitutive equations are developed to give unique stiffness responses to both the ECM and the myocytes. The micromorphic model is calibrated for cardiac tissue, first using triaxial shear experiments [80], and subsequently, to a pressure-volume relationship. The contribution of the micromorphic additional degrees of freedom to the various triaxial shear modes is quantified, and an analytical explanation is provided for differences in contributions. The passive filling phase of the heart cycle is investigated using a patient-specific left ventricle geometry supplied by the Cape Universities Body Imaging Centre (CUBIC) [38].

The formulation of a generalized trapezoidal rule for the integration of the constitutive equations for a convex elastic-plastic solid is presented. This rule, which is based on an internal variable description, is consistent with a generalized trapezoidal rule for creep. It is shown that by suitable linear extrapolation, the standard backward difference algorithm can lead to this generalized trapezoidal rule or to a generalized midpoint rule. In either case, the generalized rules retain the symmetry of the consistent tangent modulus. It is also shown that the generalized trapezoidal and midpoint rules are fully equivalent in the sense that they lead to the establishment of the same minimum principle for the increment. The generalized trapezoidal rule thus inherits the notion of B-stability and both rules offer the opportunity to exploit the second order rate of convergence for a = ½. However, in the generalized trapezoidal rule, the equilibrium. and constitutive equations are fully satisfied at the end of the time increment. This may be more convenient than the generalized midpoint rule, in which equilibrium and plastic consistency are satisfied at the generalized midpoint. A backward difference return algorithm for piecewise linear yield surfaces is then formulated, with attention restricted to an associated flow rule and isotropic material behavior. Both the Tresca and Mohr-Coulomb yield surfaces with perfectly plastic and linear hardening rules are considered in detail. The algorithm has the advantage of being fully linked to the governing principles and avoids the inherent problems associated with corners on the yield surface. It is fully consistent in that no heuristic assumptions are made. The algorithm is extended to include the generalized trapezoidal rule in such a way that the general structure of the backward difference algorithm is maintained. This allows both for the computational advantages of the generalized trapezoidal rule to be utilized, and for a basis for comparison between this algorithm and existing backward difference algorithms to be established. Using this fully consistent algorithm, the return paths in stress space for the Tresca and Mohr-Coulomb yield surfaces with perfectly plastic and linear hardening rules are identified. These return paths thus provide a basis against which heuristically developed algorithms can be compared.

The dynamics and wear of non-linear impact oscillators, comprising a single-degree of freedom system as well as continuous beam systems are analysed. The considered beams are of cantilever type with the lateral motion of the free end constrained by elastic supports. They are modelled as Bernoulli beams with Rayleigh damping. A finite-element method is used for discretisation in space and Newmark's method for time integration. Wear is quantified using the work-rate concept. The model calculations are compared with measurements of contact forces and displacements made on a loosely supported nuclear fuel rod span subject to both harmonic and random excitation. Details of the vibro-impact dynamics in the time domain are well reproduced in the digital simulations. Work-rates computed from measured and simulated quantities are also in good agreement. Furthermore, the dynamics of vibro-impacts are characterised through global and local stability and bifurcation analysis. Global analysis is made by extensive time integration for both harmonic and stochastic excitation. The local analysis is made by way of a Poincaré mapping method relating the states at subsequent impacts at the elastic supports for harmonically excited systems. The domains of stability are mapped out and the work-rate at stable periodic orbits is examined. / Godkänd; 2001; 20070225 (ysko)

This licentiate thesis is devoted to shape measurements using two different optical methods. The first one is a classical triangulation method, which uses projected fringes. The second one is a new interferometric method, which uses wavelength scanning. Both are whole field measuring methods. The main goal of the project has been to analyse the performance of an analysis scheme for absolute shape measurements called temporal phase unwrapping. This method permits the user to determine the absolute distance from the detector (usually a CCD-detector) to the object. A generalised version of the temporal phase unwrapping scheme is called reduced temporal phase unwrapping. The scheme uses an arbitrary number of fringe maps with varied fringe pitch, to calculate phase (shape). A thorough investigation is made of the performance of this algorithm. A single channel and a multi channel approach is considered. Expressions are found that relates the physical quantities to phase errors. In these simulations the single channel approach was found to be the most robust one. Expressions that relate the measurement accuracy and the unwrapping reliability, respectively, to the reduction of the fringe sequence were also found. As expected the measurement accuracy is not affected by a shorter fringe sequence while a significant reduction in the unwrapping reliability is found, as compared to the complete negative exponential sequence. The strength of reduced temporal phase unwrapping is demonstrated experimentally, in a projected fringe three-channel system. Instead of letting each channel carry phase-stepped images each channel can carry images with a change in fringe pitch. This significantly reduces noise, but at least three images needs to be acquired. It is also shown that the temporal phase unwrapping analysis scheme can be used to evaluate experimental data from wavelength scanning interferometry. Two unwrapping strategies are considered: fitting to a reversed exponential sequence and complex Fourier-transform ranging. The achievable accuracy for both methods ultimately depend on the tuning width, the speckle correlation, and random noise in the optical setup. / Godkänd; 2000; 20070318 (ysko)

<p>Godkänd; 1998; 20070404 (ysko)</p>