The current thesis work details a non-contact detection approach concerningclassification of snow with different physical properties such as grain size, densityand specific surface area (SSA). In this approach, reflected light from snowsurfaces is measured as a function of wavelength and viewing geometry. Essentiallya detector (either a near-infrared (NIR) camera or a spectrometer) and anillumination source are needed to measure the spectrally and angularly resolvedbidirectional reflectance from snow. Classification of snow types is performedbased on the absorption and scattering properties of a respective snow type. Itis furthermore known that snow properties can be modelled using a numericalsolver where the radiative transfer equation (RTE) for snow is solved and ascattering phase function is estimated by expanding into a series of Legendrecoefficients. It is therefore expected to be a connection between snow characteristicsand the Legendre coefficients of the scattering phase function. Results suggest that different snow types can be classified using two wavelengths(980 nm, 1310 nm) from the high reflectance region and one wavelength(1550 nm) from the high absorption region. It is also observed that thebidirectional reflectance for snow tends to increase in specular direction (antiilluminationdirection) as snow density increases. Results from the numericalmethod suggest that the first coefficient of the Legendre phase function is arelative estimate of the single scattering albedo rather than an absolute estimateand that the second coefficient estimates the anisotropy of a respectivesnow type. Investigations in this thesis suggest that the presented approachcan be used as a tool to classify different snow types in various applicationssuch as icing on wind turbine blades, winter roads maintenance and ski tracksmaintenance.v

This thesis focuses on two main topics, the physics governing how faults rapidly weaken during an earthquake and the thermal and mechanical structure of ice stream shear margins. The common theme linking these two projects is the desire to understand how the complicated interactions between stress and temperature control deformation and failure. All of the problems in this thesis are attacked using a combination of analytic and numerical methods, and the interplay between these two approaches provides a powerful way to understand the different physical balances that dominate in different regimes. We also use aspects of materials science to understand how the often complicated rheologies are controlled by underlying physical phenomena such as melting, phase transitions, diffusion, and dislocation motion. With regards to fault mechanics, we begin by showing how co-seismic weakening mechanisms driven by elevated pore fluid pressures lead to micron-scale strain localization during an earthquake. We solve for the localized zone thickness for a range of fault temperatures, test these predictions using numerical simulations, and show how the onset of localization accelerates fault weakening. Next we present the first solutions to account for thermal decomposition reactions during a dynamic rupture, showing that the activation of thermal decomposition may lead to a larger slip duration and total slip. Finally we present a new set of experiments studying flash heating of serpentinite, highlighting the dependence of friction on normal stress and the presence of gouge, and producing the first model to explain the hysteresis commonly observed in flash heating experiments. With regards to ice stream shear margins, we begin by extending the work of Perol and Rice [2011] to study the formation of temperate ice in shear margins, and quantify the total melt that may be generated within the shear margins. We conclude by investigating how the presence of such a channel alters the stress on and strength of the undeforming bed in the shear margin, showing that the transition from a deforming to an undeforming bed across a channel is stable when the water flux in the channel exceeds a critical value.

The rules and mechanical forces governing cell motility and interactions with the extracellular matrix of a tissue are often critical for understanding the mechanisms by which breast cancer is able to spread through the breast tissue and eventually metastasize. Ex vivo experimentation has demonstrated the the formation of long collagen fibers through collagen gels between the cancerous mammary acini responsible for milk production, providing a fiber scaffolding along which cancer cells can disorganize. We present a minimal mechanical model that serves as a potential explanation for the formation of these collagen fibers and the resultant motion. Our working hypothesis is that cancerous cells induce this fiber formation by pulling on the gel and taking advantage of the specific mechanical properties of collagen. To model this system, we present a hybrid method where we employ a new Eulerian, fixed grid simulation known as the Reference Map Method to model the collagen as a nonlinear viscoelastic material coupled with a multi-agent model to describe individual cancer cells. We find that these phenomena can be explained two simple ideas: cells pull collagen radially inwards and move towards the tension gradient of the collagen gel, while being exposed to standard adhesive and collision forces. From a computational perspective, we hope that our work can serve as a generalizable framework for future theoretical studies of the mechanical interactions between a large number of cells and a dynamic environment.

A variety of instabilities can be triggered when elastic structures are subjected to mechanical loadings. While such instabilities have traditionally been considered as a failure, a new trend is emerging in which the dramatic geometric changes induced by them are harnessed to enable new functionalities. In this thesis, I report a systematic study on the morphology and functionality changes induced by buckling in soft structures. Using a combination of theoretical, numerical and experimental analyses, I investigate the non-linear response of a variety of one dimensional, two dimensional and three dimensional systems, with particular emphasis on their stability. The results show that the deformation induced by buckling can be rather complex even if the undeformed geometry is simple. Moreover, I demonstrate that a wide range of morphologies can be obtained by carefully controlling the geometric, material and loading parameters. Such tunability may open venues for the design of structures with adaptive and switchable properties. / Engineering and Applied Sciences - Engineering Sciences

In manufacturing industry there is a high demand for on line quality control to minimize the risk of incorrectly produced objects. Conventional contact measurement methods are usually slow and invasive, meaning that they cannot be used for soft materials and for complex shapes without influencing the controlled parts. In contrast, interferometry and digital holography in combination with computers become faster, more reliable and highly accurateas an alternative non-contact technique for industrial shape evaluation. For example in digital holography, access to the complex wave field and the possibility to numerically reconstruct holograms in different planes introduce a new degree of flexibility to optical metrology. With digital holography high resolution and precise three dimensional (3D) images of the manufactured parts can be generated. This technique can also be used to capture data in asingle exposure, which is important when doing measurements in a disturbed environment. The aim of this thesis is devoted to the theoretical and experimental development of shape and deformation measurements. To perform online process control of free-form manufactured objects, the measured shape is compared with the CAD-model to obtain deviations. To do this, a new technique to measure surface gradients and shape based onsingle-shot multiplexed dual-wavelength digital holography and image correlation of speckle displacements is demonstrated. Based on an analytical relation between phase gradients and speckle displacements it is shown that an object is retrieved uniquely to shape, position and deformation without the unwrapping problems that usually appear in dual-wavelength holography. The method is first demonstrated using continues-wave laser light from twotemperature controlled laser diodes operating at 640 nm. Then a specially designed dual core diode pumped fiber laser that produces pulsed light with wavelengths close to 1030 nm is used. In addition, a Nd:YAG laser with the wavelength of 532 nm is used for 3D deformation measurements. One significant problem when using the dual-wavelength single-shot approach is that phase ambiguities are built in to the system that needs to be corrected. An automatic calibration scheme is therefore required. The intrinsic flexibility of digital holography gives a possibility to compensate these aberrations and to remove errors, fully numerically without mechanical movements. In this thesis I present a calibration method which allows multiplexed singleshotonline shape evaluation in a disturbed environment. It is shown that phase maps and speckle displacements can be recovered free of chromatic aberrations. This is the first time that a multiplexed single-shot dual-wavelength calibration is reported by defining a criteria tomake an automatic procedure. Further, Digital Speckle Photography (DSP) is used for the full field measurement of 3D deformations. In order to do 3D deformation measurement, usually multi-cameras and intricate set-up are required. In this thesis I demonstrate the use of only one single camera torecord four sets of speckle patterns recorded by illuminating the object from four different directions. In this manner, meanwhile 3D speckle displacement is calculated and used for the measurement of the 3D deformations, wrapping problems are also avoided. Further, the same scale of speckle images of the surface for all four images is guaranteed. Furthermore, a need for calibration of the 3D deformation measurement that occurs in the multi-camera methods,is removed. By the results of the presented work, it is experimentally verified that the multiplexed singleshot dual wavelength digital holography and numerically generated speckle images can be used together with digital speckle correlation to retrieve and evaluate the object shape. Usingmultidirectional illumination, the 3D deformation measurements can also be obtained. The proposed method is robust to large phase gradients and large movements within the intensity patterns. The advantage of the approach is that, using speckle displacements, shape and deformation measurements can be performed even though the synthetic wavelength is out of the dynamic range of the object deformation and/or height variation. / Godkänd; 2016; 20160126 (davkho); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Davood Khodadad Ämne: Experimentell mekanik /Experimental Mechanics Avhandling: Multiplexed Digital Holography Incorporating Speckle Correlation Opponent: Professor Pascal Picart, ENSIM-École Nationale Supérieure d’Ingénieurs du Mans, LeMans, Frankrike. Ordförande: Professor Mikael Sjödahl, Avd för strömningslära och experimentell mekanik, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet, Luleå. Tid: Torsdag 25 februari, 2016 kl 10.00 Plats: E231, Luleå tekniska universitet

The common 3-point safety belt usually has some anchor points on the car body. However, it is also possible to mount all anchor points on the seat structure. In general, different studies show some advantages with seat integrated safety belts. Thus, further investigations are motivated. One safety advantage appears in the case of so-called small overlap crashes. Also, the ride-down distance of the occupant may be increased by allowing controlled energy absorbing deformation of the seat structure. Further, methods that can be used to minimize the weight of seat structures with integrated safety belts are of interest. A complement to full scale crash tests is the use of numerical models and numerical simulation, typically finite element (FE) analysis. Research and development of numerical models are constantly improved. In general, any type of numerical model needs to be evaluated to physical tests in order to make it behave as realistic as possible. The purpose of the present thesis was to study seat structures with integrated safety belts with a design that may intentionally deform and absorb energy during a crash. The approach was to use numerical models and numerical simulation and to investigate both biomechanical and mechanical responses. The aim is to create a basis for future research in the design of seat structures with integrated safety belts. In Paper A and B, parametric studies comparing integrated 3- and 4-point safety belt configurations relative to common 3-point configurations are presented. A number of mechanical parameters were varied. Biomechanical responses of the Hybrid III (HIII) FE-dummy model used as occupant were studied. In Paper C, the creation and evaluation of a human FE-model of a 50th percentile male is presented. The evaluation was made to results from studies with post mortem human subjects (PMHS). In Paper D, a conceptual methodology for mass minimization of a property based model (PBM) of a seat structure with an integrated 3-point safety belt configuration and with a HIII FE-dummy model used as occupant is presented. Both mechanical and biomechanical constraints were used as well as different start values of the design variables. In Paper E, the evaluation of FE-models of simplified seat structures with integrated 3-point safety belt configurations to a number of full scale experiments in the form of sled tests with a HIII crash test dummy used as occupant is presented. The studies in Paper A and B reveals that with an adequate combination of mechanical properties of the seat structure it should be possible to achieve equal or lower biomechanical responses of the occupant with a seat integrated safety belt configuration compared to a common. The seat integrated 4-point configurations in these studies performed poorer than the corresponding 3-point in general. An important issue is that belt- webbing distribution between lap and torso belt parts is allowed. The study in Paper C showed that the created and evaluated human FE-model could be used to further explore injury producing mechanisms. However, in order to achieve a fully evaluated human FE-model there is a need for both further development and more reference tests with PMHS. In Paper D, the study showed that the presented methodology may be used in a concept phase of a design process. The optimization runs with different start values of the design variables found a number of different local minima instead of one global minimum. The dynamics of the system was highly non-linear. To find an optimal combination of mechanical properties and biomechanical responses, a compromise appears to be needed. The evaluated FE-model in Paper E may be used in simulations that consider both biomechanical and mechanical responses. The majority of the simulated responses showed good agreement with or slightly underestimated the experimental responses. Some issues of the FE-model suggest areas for further development. The FE-model could be used as a base for further studies. / Godkänd; 2008; 20080404 (ysko)

Denna rapport skall ses som en genomförbarhetsstudie för ett 4.5kW kraftaggregat som är avsett att operera i mycket stränga industriella miljöer. På grund av detta är hela aggregatets inre volym tätat från yttre åverkan och problemen aggregatet utsätts för är alltså både mekanisk påverkan i form av vibrationer och chock samt termisk påfrestning då kylning via insugningsluft är uteslutet. Lösningen för detta var att dimensionera och fixera mekaniken på ett tillfredställande sätt och även att kyla aggregatets alla effektbärande komponenter via vätskekylning i kombination med intern temperaturfördelning med en eller två cirkulationsfläktar. Resultatet blev principerna för ett gediget kraftaggregat som är ytterst motståndskraftig mot vibrationer och inkluderar därmed ett kylningsförfarande som kan motstå de mycket stränga temperaturstegringarna aggregatet kan tänkas utsättas för. / This report could be summarized as a feasibility study for a 4.5kW power supply which shall operate in a very harsh industrial environment. All internal components of the power supply are sealed from external damage because of this fact. The problem the power supply has to endure are both mechanical in form of vibrations and shock but also thermal since external intakes for a standard “fan cooling” solution is impossible. The solution was to scale the dimensions and fix the construct in a way that would prevent this type of mechanical damage and also use a fluid cooling solution from an external source where the cooled air inside will circulate thanks to a couple of internal fans. The result is a sturdy power supply design resistant to vibrations and with a cooling solution that can withstand the very harsh temperature situations this construct could be exposed to. / Termisk och mekanisk idégenerering med hjälp av datorsimuleringar

Membrane structures are commonly used in many fields. The studies of these structures are of increasing interest. The projects in this thesis focus on the evaluations of equilibrium states for pressurized membranes under different problem settings, using finite element methods, and the corresponding instability behaviors. The first part of the current work discusses the instability behavior of a thin, planar, circular and initially horizontal membrane subjected to downwards or upwards fluid pressure. The membrane structures exhibit large deformations under pressure. The method for evaluating fluid pressure from gravity was developed in finite element context, and used in numerical simulations. Limit and bifurcation points have been detected for different loading parameters and conditions. The effects on instabilities of parameters, the initial states of the membrane, and the chosen mesh are discussed. The second part of the current work discusses instability behavior of a thin, spherical and closed membrane containing gas and fluid, when placed on a horizontal rigid and non-friction plane. A multi-parametric loading is described. By adding practically relevant controlling equations, different classes of equilibrium paths were followed using a generalized path following algorithm. Stability conclusions were made, according to the considered load parameters and the constraints. A generalized eigenvalue analysis was used to evaluate the stability behavior including the constraint effects. Fold line evaluations were performed to analyze the parametric dependence. A solution surface approach is used to visualize the mechanical response under this multi-parametric setting. The third part of the current work focuses on instability response of a truncated sphere, containing gas and fluid, and in contact with two vertical rigid and non-friction planes. Different penalty formulations were used and compared. The effects of contact implementations on instability behaviors were investigated. Bifurcation points induced by contacts have been observed. Multi-parametric problems were defined, and generalized paths were followed. The multi-parametric stability was evaluated using generalized eigenvalue analysis, based on the mass and total differential matrices. The effects of augmenting equations on bifurcation points and limit points are discussed. The fourth part of the current work analyses the instability response of a truncated sphere, completely filled with fluid, placed on a horizontal plane and spinning around the vertical axis. The loads from fluid pressure and the constraints, e.g., fluid volume, were formulated to generate a symmetric differential matrix. Several mesh patterns with different symmetries were used to simulate the model, and the obtained results are compared. Various problem settings were considered, and generalized paths were followed. The effects of symmetry aspects of the chosen meshes on instability behaviors are discussed, as are the effects of parameters. / <p>QC 20170616</p>

No description available.

There is a strongly increasing request of measuring systems for mechanical properties studies, for example in the paper industry. Paper research is today not only concentrated to flock studies, weight and quality controls of the paper but also focussing of mechanical behaviours in the fibre scale. For this purpose, an optical metrology system for measurements of mechanical response in the µm-range of loaded sub-mm objects is developed, but the system could also be used for materials like polymer composites, wood or steel. The system is full-field, non-touching and all-electronic. The main components in the system are a stereomicroscope and a speckle correlation technique called digital speckle photography. Either a random structure pattern exists naturally on the sample or a dot pattern must be attached on its surface. Using white light illumination, 2-D and 3-D deformation fields as well as velocity fields can be measured. The standard deviations are about 60 nm in plane and about 170 nm out of plane, depending on the magnification and quality of the pattern. Information of the topography of the sample is provided in the calibration routine for 3-D measurements. By using laser illumination, measurements of microstructural changes on the object surface are possible through a technique called laser speckle decorrelation. Examples of measurements of micro-flow, 3D deformations and microstructural changes in printing paper are given in this thesis. / Godkänd; 2002; 20070222 (ysko)