Abstract This thesis deals with the analysis of the rheological structure and tectonic modelling of the Fennoscandian Shield. First, a short introduction to the geology and geophysics of the Fennoscandian Shield is presented followed by a description of rheological concepts. Second, the applied modelling procedures, together with the sources of error are explained. Last a brief summary of each original paper including conclusions is given. Understanding rheological conditions through the entire lithosphere and even deeper is the key for understanding the deformation of the earth's interior. Thus, investigating the rheological structure and possible consequences resulting from tectonic loading are required to some extent when interpreting geophysical data into tectonic models. In this thesis rheological structure is obtained by calculating rheological strength in different locations of the central Fennoscandian Shield. These locations are mainly situated along different deep seismic sounding (DSS) profiles as they provide necessary geophysical information required for model construction. Modelling begins by solving the thermal structure in the lithosphere, as rheological behaviour, mainly ductile flow is strongly controlled by temperature. Results from these calculations show that the rheological structure of the lithosphere depends on the thermal conditions resulting in significant areal variations. Generally, the central Fennoscandian Shield can be considered to be rheologically rather strong. Rheologically weak layers are however usually found in the lower crust. Correlation of the rheological structure with earthquake focal depth data shows that brittle fracture is the relevant mechanism in the earthquake generation and that non-occurrence of deep earthquakes implies low stress or high strength conditions deeper in the crust. Calculated rheological structure is furthermore used as a material parameter in the structural models which are solved next. These results suggest that it is highly unlikely that any considerable ductile deformation in the crust of the central Fennoscandian Shield exists and it seems that the present-day thermal and mechanical conditions in the investigated area do not favour such processes in significant amounts.

No description available.

D.Ing. (Mechanical Engineering) / The local buckling of axially loaded thin walled circular aluminium tubes is investigated in this work. Various buckling modes can be identified depending on certain geometrical ratios. Tubes with a thickness to diameter ratio of between 0,016 and 0,1 will buckle according to the so called axi-symmetric mode which is a very efficient collapse mechanism for energy absorbing purposes. Although there are numerous analytical solutions for this collapse mode the results are not fully descriptive. A finite-element model was developed and is described in this work. With this model it is possible to analyse the collapse mechanism in detail and the results obtained compare favourably with experimental values. When a relatively long thin walled tube is loaded axially it will undergo Euler buckling. This is not an effective collapse mechanism for energy absorbing purposes and a concept that overcomes this disadvantage is presented. With this energy absorber it is possible for axially loaded longthin walled circular tubes to collapse into a mode that resembles the axi-symmetric collapse mode. A finite element model was developed and successfully used to analyse the proposed concept. The results obtained correlate well with experimental values. A low speed impact test rig was designed, manufactured and commissioned. This rig was used to conduct dynamic tests on the proposed energy absorber and it was concluded that the proposed concept is viable for applications that require an inexpensive, reliable energy absorber with a long strokelength.

The energy convergence of mixed methods of approximate analysis for problems involving linear self-adjoint operators is investigated. A new energy product and the associated energy norm are defined for such indefinite systems and then used in establishing the strain energy convergence and estimation of error for problems in continuum mechanics. In the process, the completeness requirements are laid out for approximate solutions. Also established is the mean convergence of the basic variable e.g. displacements and stresses. After accomplishing a new mathematical framework for the mixed methods in continuum, the theory is then extended to the finite element method. The completeness requirements, convergence criteria and the effect of continuity requirements on convergence are established. The flexibility offered by the mixed methods in incorporating the boundary con ditions is also demonstrated. For stress singular problems, the strain energy convergence is established and an energy release method for determining the crack intensity factor K. is presented. A detailed eigenvalue-eigenvector analysis of the mixed finite element matrix is carried out for various combinations of interpolations for the plane stress linear elasticity and the linear part of the Navier-Stokes equations. Also discussed is its relation to the completeness requirements. Finally, numerical results are obtained from applying the mixed finite element method to several examples. These include beam bending, a plane stress square plate with parabolically varying end loads, a plane stress cantilever and plane strain stress concentration around a circular hole. A plane stress example of a square plate with symmetric edge cracks is also solved to study the strain energy convergence. Lastly, two rectangular plates, one with symmetric edge cracks and the other with a central crack are considered to determine the crack intensity factor K. In most of the examples, the strain energy convergence rates are predicted and compared with the numerical results, and excellent agreement is observed. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.