No description available.

Granular materials are very common both in nature and in industry, and their extensive use means that there are financial incentives for increased efficiency. There are huge costs related to their use and handling, which is a major motivation for increased knowledge of the behaviour of granular materials at different loading conditions. The development of tools for numerical simulation of granular materials at diverse flow conditions gives the opportunity to study and optimise various industrial processes. In order for such tools to be trustworthy, calibration and validation against experimental results is essential. Thus, experimental methods for accurate measurement and characterisation of granular material flow are required. The objective of this thesis is to contribute to the knowledge of experimental characterisation and numerical modelling of non-cohesive, dry granular materials, at dissimilar flow conditions. In order to fulfil this objective, an experimental method, able to capture the flow behaviour of granular materials is developed. The method is based on the digital image correlation technique, and it is used for field measurements of displacement and velocity. The devised method is used to obtain field measurements for the flow of sand, tungsten carbide powder and potassium chloride. For modelling and simulation, the smoothed particle hydrodynamics (SPH) method, and a pressure-dependent, elastic-plastic constitutive model are used. In this thesis, experimental characterisation and numerical modelling of granular material flow is performed in a number of applications. An experimental powder filling rig is used to study the flow during filling of sand into a die. A high-speed digital camera is used to record the flow, and the digital image correlation technique is used to obtain field measurements during the filling. This method is also applied in another experimental setup, where flow during filling of spherical tungsten carbide powder into a die is studied. The filling of tungsten carbide powder is simulated using the SPH method, and the results are compared to the field measurements with good agreement. Furthermore, the flow of potassium chloride is studied experimentally in the collapse of a granular column and in the discharge from a flat bottomed silo. The material flow process in both the column collapse and silo discharge are simulated using the SPH method. The results from simulations are found to be in agreement with observations reported in literature, and with experimental measurements obtained in this work. In conclusion, an experimental method for characterising granular material flow through field measurements is presented. The method is used to support the exploration of numerical tools for modelling and simulation of granular material flow. Furthermore, the high accuracy field measurements are used for improved calibration and validation of numerical methods. Reliable numerical simulations allows for study of the mechanisms that are present during granular material flow, mechanisms that might be hard or even impossible to investigate experimentally. The work within the present thesis contributes to the knowledge of both experimental characterisation and numerical modelling of granular material flow.

No description available.

<p>Upprättat; 2016; 20160705 (stegol)</p>

Sintering at high-pressure improves the properties of the material, either through new sintering aids becoming available or through improving intergranular bonding. This gives the manufactured products potential advantages like faster cut rates, and more precise and cleaner production methods that add up to cost efficiency and competitive edge. The production of synthetic diamond products demands tooling that can achieve high pressures and deliver it with a high degree of certainty. The common denominator for almost all high-pressure systems is to use capsules where a powder material encloses the core material. Numerical analysis of manufacturing processes with working conditions that reach ultra high pressure (above 10 GPa) requires a constitutive model that can handle the specific behaviours of the powder from a low density to solid state. The work in this thesis deals with characterization and simulation of the material behaviour during high-pressure compaction in powder pressing. Some of the work was focused on investigating the material when used as compressible gasket in high-pressure systems. The aim was to increase the knowledge of the high-pressure pressing process. This includes a better understanding of how mean stress develops in the compact during pressing and an insight into the development material models concerning highpressure materials. Both experimental and numerical investigations were made to gain knowledge in these fields. The mechanical behaviour of a CaCO3 powder mix was investigated using the Brazilian disc test, uniaxial compression testing and closed die experiments. The aim of the experimental work was to provide a foundation for numerical simulation of CaCO3 powder compaction at higher pressures. Friction measurements of the powder were also conducted. From the experimental investigations, density dependent material parameters were found. An elasto-plastic Cap model was developed for ultra high-pressure powder pressing. To improve the material model, density dependent constitutive parameters were included. The model was implemented as a user-defined material subroutine in a nonlinear finite element program. The model was validated against pressure measurements using phase transitions of Bismuth. The measurements were conducted in a Bridgman anvil apparatus. The simulations showed that thin discs with small radial extrusion generate a plateau at a low-pressure level, while thick discs with large radial extrusion generate a pressure peak at a high-pressure level. The results showed that FE-results can be used to engineer pressure peaks needed to seal HPHT-systems. For compressible gaskets, it was found that diametral support increases the phase transformation load. Higher initial density of the powder compact and diametral support generate higher pressure per unit thickness. The results from the validation using pressure measurements showed that the simulation model was indeed capable of reproducing load–thickness curves and pressure profiles, up to 9 GPa, close to the experimental curves. / Godkänd; 2011; 20111020 (bersve); DISPUTATION Ämnesområde: Hållfasthetslära/Solid Mechanics Opponent: Professor Javier Oliver, Dept of Strength of Materials and Structural Analysis, Technical University of Catalonia, Barcelona, Spain, Ordförande: Bitr professor Pär Jonsén, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Torsdag den 15 december 2011, kl 09.00 Plats: E246, Luleå tekniska universitet

Shearing is the process where sheet metal is mechanically cut between two tools. Various shearing technologies are commonly used in the sheet metal industry, for example, in cut to length lines, slitting lines, end cropping etc. Shearing has speed and cost advantages over competing cutting methods like laser and plasma cutting, but involves large forces on the equipment and large strains in the sheet material. The constant development of sheet metals toward higher strength and formability leads to increased forces on the shearing equipment and tools. Shearing of new sheet materials imply new suitable shearing parameters. Investigations of the shearing parameters through live tests in the production are expensive and separate experiments are time consuming and requires specialized equipment. Studies involving a large number of parameters and coupled effects are therefore preferably performed by finite element based simulations. Accurate experimental data is still a prerequisite to validate such simulations. There is, however, a shortage of accurate experimental data to validate such simulations. In industrial shearing processes, measured forces are always larger than the actual forces acting on the sheet, due to friction losses. Shearing also generates a force that attempts to separate the two tools with changed shearing conditions through increased clearance between the tools as result. Tool clearance is also the most common shearing parameter to adjust, depending on material grade and sheet thickness, to moderate the required force and to control the final sheared edge geometry. In this work, an experimental procedure that provides a stable tool clearance together with accurate measurements of tool forces and tool displacements, was designed, built and evaluated. Important shearing parameters and demands on the experimental set-up were identified in a sensitivity analysis performed with finite element simulations under the assumption of plane strain. With respect to large tool clearance stability and accurate force measurements, a symmetric experiment with two simultaneous shears and internal balancing of forces attempting to separate the tools was constructed. Steel sheets of different strength levels were sheared using the above mentioned experimental set-up, with various tool clearances, sheet clamping and rake angles. Results showed that tool penetration before fracture decreased with increased material strength. When one side of the sheet was left unclamped and free to move, the required shearing force decreased but instead the force attempting to separate the two tools increased. Further, the maximum shearing force decreased and the rollover increased with increased tool clearance. Digital image correlation was applied to measure strains on the sheet surface. The obtained strain fields, together with a material model, were used to compute the stress state in the sheet. A comparison, up to crack initiation, of these experimental results with corresponding results from finite element simulations in three dimensions and at a plane strain approximation showed that effective strains on the surface are representative also for the bulk material. A simple model was successfully applied to calculate the tool forces in shearing with angled tools from forces measured with parallel tools. These results suggest that, with respect to tool forces, a plane strain approximation is valid also at angled tools, at least for small rake angles. In general terms, this study provide a stable symmetric experimental set-up with internal balancing of lateral forces, for accurate measurements of tool forces, tool displacements, and sheet deformations, to study the effects of important shearing parameters. The results give further insight to the strain and stress conditions at crack initiation during shearing, and can also be used to validate models of the shearing process.

No description available.

This thesis presents an optical method to measure the rolling friction coefficientsfor balls rolling freely on a cylindrical surface. Two different models of a ball rollingfreely on a cylindrical surface are established, one is an analytical model and the otheris a numerical model derived from Lagrange equation. The rolling friction coefficientsare evaluated from the position data of the steel balls. The positions data are retrievedfrom images recorded by a high-speed camera. The locating algorithms includingbackground subtraction and ball recognition are presented in detail. The rollingfriction coefficients between different diameter steel balls and a cylindrical aluminumsurface are measured. The angular positions of the balls are predicted by the solutionof the equation of motion (EOM), and good agreements are found between theexperimental and theoretical results. The values of rolling friction coefficientsbetween different diameter steel balls and a cylindrical aluminum surface areevaluated.

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

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