n development of bumper systems for the automotive industry, iterative Finite Element (FE) simulations are normally used to find a bumper design that meets the requirements of crash performance. The crash performance of a bumper system is normally verified by results from standardized low speed crash tests based on common crash situations. Consequently, these crash load cases are also used in the FE simulations during the development process. However, lack of data for the car under development implies that simplified models must be used as a representation of the car in the FE simulations. Present simplified models of the car lead to uncertainties of the design even though the bumper system is modelled in a proper manner. The present work focuses on methods of how to represent the car in the FE crash simulations. The work is limited to the standardized crash tests in which the force acts longitudinally along the vehicle. Two different types of modelling perspectives are investigated. With the traditional approach, the aim is to obtain agreement of the results from the FE simulation and the physical test in terms of force from the barrier as a function of the compression of the bumper system. Here, the vehicle is represented by a point mass connected via rigid beam elements to the bumper system. The point mass, which only is allowed to translate longitudinally, is assigned with a reduced mass compared to the physical mass of the car to compensate for energy transformations in the car during the collision. In paper A, it is shown that the required mass reduction is dependent on vehicle and bumper characteristics as well as on the loading conditions. Also, the simple method of mass reduction leads to difficulties in attaining high agreement for time history of force and compression. In contrast to this, the idea with the second modelling technique is to reach a high agreement of the time history of force and compression of the bumper system. This methodology is based on a model structure that consists of mass elements, linear spring and viscous damper elements. It is shown that this model structure can provide high agreement between the FE simulation and the physical crash test in terms of force and compression as functions of time even for different loading conditions without adjusting the model parameters. Within the current thesis, a methodology of identifying parameters in the Mass Spring Damper (MSD) model from physical crash tests is presented. The methodology identifies a set of parameters that minimizes the deviation of the resulting displacements from the crash test and the simulation. This identification methodology is then used in a Design of Experiments (DOE) approach for relating model parameters in the MSD model to general properties of an arbitrary vehicle such as axial stiffness, bending stiffness and mass. For this, a public domain FE simulation model of a Ford Taurus is used. The knowledge gained from this study makes it possible to use the MSD model for representation of a coming car in the FE simulations associated with bumper development. / <p>Godkänd; 2006; 20061120 (pafi)</p>

In the vehicle industry there is a constant struggle to develop cars with high passive safety without increasing the fuel consumption. High passive safety requires a very rigid behaviour of the crash protecting components. Accomplishing this often leads to an increase in the weight of the components. An increase in weight results in a higher fuel consumption which is bad for the environment as well as for the economy of the car owner, therefore the manufacturers turn to new materials. One of these new materials is ultra high strength steel which is the material in focus for the present thesis. To be able to utilize all the advantages of ultra high strength steel the material behaviour must be investigated in detail. In this thesis, sheets of ultra high strength steel, which are produced by press-hardening, are investigated using a method called digital speckle photography. When using the method of digital speckle photography (DSP) a series of photographs are taken of a deforming specimen. Prior to the experiment a random pattern (speckles) has been applied to the specimen and by studying the deforming speckle pattern on the images, the deformation fields through time can be established. Within the present thesis the deformation fields up to the point of fracture have been investigated on a length scale of the order of 10e-4 meters. With length scales of this magnitude the deformation inside a localized neck can be investigated. This is done, both for a specimen shape that induces a fracture initiation at an inner point of the specimen and a specimen shape where fracture starts from the edge of a hole. These investigations show that there is a strong localization of the strain before fracture is initiated. The local strain values inside a localized neck are significantly higher than the strain values that can be observed with conventional experimental techniques involving extensometers. It is also noticed that the method used to make holes play an important role for the onset of fracture. Some methods hardly affect the material at all while others can decrease the level of local strain at the onset of fracture down to about a third of the value for unaffected material. Furthermore, a method for characterizing the material based on full-field measurements is presented. The method is a fast and simple alternative to previously used inverse modelling procedures where the material model of a finite element simulation is updated iteratively to make the simulation produce the same results as the experiment. / <p>Godkänd; 2007; 20070514 (ysko)</p>

In recent years an increasing interest has evolved concerning seat integrated safety belts in cars, regarding both 3- and 4-point belts in various configurations. One safety advantage of seat integrated safety belts appears in the case of so-called small overlap crashes. One consequence of a small overlap crash can be that the colliding cars strike each other's sides hitting both the A- and B-pillar. Hence, the A- as well as the B-pillar are pushed inwards and backwards. In this case, belt anchor points on the B-pillar may also be pushed backwards and the belt will be stretched over the occupant. The purpose of the present study was to investigate seat integrated safety belt configurations that may involve a seat structure design that intentionally deforms and absorbs energy during a crash. Common 3-point configurations were used as references. The aim was to investigate how the physical properties influence the interaction of the seat back frame and the safety belt. Numerical simulations were carried out using the explicit LS-DYNA FE-analysis software. A FE-model of a seat structure, floor pan and B-pillar was established. A 50th percentile Hybrid III FE-dummy model was used as occupant and for studying the biomechanical responses. Different physical properties of the seat structure and different belt load limit forces were used as parametric variables. Only frontal crashes were considered. Responses concerning chest deflection, head- and chest displacement, change of pelvis angle, pelvis submarining tendency, lap- and torso belt forces, seat back frame deflection, ride-down efficiency, seat structure natural frequency, upper neck loads and neck injury criteria were studied. The results indicate that the belt-webbing distribution between the lap and the torso belts via a slip-ring and in combination with a non-rigid seat back frame increases the ride-down efficiency compared to a system with no belt-webbing distribution. Further, the combined use of different energy absorption mechanisms influences the biomechanical response as well as the structural response of an integrated safety belt configuration. An optimal solution with respect to multiple objectives requires a proper combination of parameters. Beside the optimisation of traditional biomechanical responses, the multiple objectives can be the minimisation of weight and cost as well as optimal control of passenger kinematics. The present study will hopefully create a basis for future research and possibly for the design of seat integrated safety belts. / <p>Godkänd; 2006; 20070109 (haneit)</p>

Handling of iron ore pellets is an important part in the converting process for LKAB. Knowledge about this sub process is very important for further efficiency progress and increased product quality. The existence of a simulation tool with modern modelling and simulation methods will significantly increase the possibility to predict the critical forces in product development processes and thereby decrease the amount of crushed pellets (fines). In this work, simulations of granular material flows on a global scale are performed. From the simulations, properties like flow pattern and density distribution are studied. The methodology is suitable for different applications of particle flows. The particles could be stones, ore, ore pellets, metal powder and other granular materials. Previous studies exploring flow patterns and stress fields in granular solids are analysed with experiments or with numerical methods such as discrete element (DE) method or finite element (FE) computations. In this work, the smoothed particle (SP) method is used to simulate granular material flow. It is a mesh-free continuum-based computational technique where each calculation node is associated with a specific mass, momentum and energy. Properties within the flow such as density and movements of the nodes results from summations via a kernel function of the neighbours of each node to solve the integration of the governing equations. The fact that there are no connections between the nodes in the SP method, results in a method that handles extremely large deformations and still has the advantages of a continuum-based method. This is a major advantage versus FE and DE analysis. Within the current thesis, two applications of simulating granular material with SP analysis is presented: iron ore pellets flow in a flat bottomed silo and simulation of shoe filling of metal powder into simple and stepped dies. In the first application, primarily the flow pattern, when discharging a silo with pellets, is studied and compared with experimental results. Next application focuses on the filling behaviour and density distribution in metal powder shoe filling. For trustworthy numerical simulations of iron ore pellets flow, knowledge about their mechanical properties is needed. In this work, an elastic-plastic material characterization for blast furnace pellets is evaluated from experimental data. Constitutive data in vein of two elastic parameters and a yield function for the pellets bulk material is determined. The present study is an important step towards a simulation tool to predict the critical load in different handling systems of pellets. / Godkänd; 2008; 20080428 (ysko)

The rapid development of computing technology has made powerful tools, such as finite element codes, available for more and more companies. The use of simulation tools, predictive engineering, is a prerequisite today in product development. To describe the material deformation a variety of constitutive models, based both on physical foundations and empirical considerations, are available. Common for all models is that they contain material parameters, which have to be estimated by utilising experimental methods. Despite the advanced numerical tools, the most common method to characterise materials in industry today is to use standard tensile tests. Those tests have a major drawback. When the loading is no longer homogenous, and plastic instability has initiated, the stress-strain relationship is no longer valid. The aim for this work is to investigate methods for parameter estimation in material models. The test material used is hot-rolled cold-forming steel. A further aim is to yield stress-strain curves more appropriate for large deformations compared to a standard tensile test. The main features are the use of experiments, finite element analysis (FEA) and inverse modelling combined. The parameter estimation is formulated as an inverse problem and an objective function, describing the residual error between experimental data and data from a FEA of the experiment, is formulated as a least-square functional. The objective function is minimised by an optimisation algorithm yielding a vector of best fit, or estimated, material parameters. Two approaches are investigated. One global, where experimental data from a forming experiment is used. Data is in the form of tool force and displacement, hence global data. This is in contrast with a local approach where in-plane full-field measurements of displacements on a flat specimen (hence, local data), subjected to a tensile test, are collected through the whole deformation history until fracture. The measurements are made with digital speckle photography (DSP). Parameters are estimated for a total of three different material models, assuming isotropic material properties and yield surface according to von Mises. Results from the global approach show significant difference in the stress-strain curves and a force response with optimised models compared to an extrapolated tensile test curve. In the local approach the DSP-technique provided measurements, where the maximum equivalent plastic strain in a specimen was approximately 0.8. The true stress-strain curves based on the estimated parameters are validated in the low strain region by comparison with curves from standard tension tests. / Godkänd; 2004; 20070115 (ysko)

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