The purpose of this work has been to investigate the ultimate capacities of aluminium plates. The aluminium plates are supposed to be part of a marine structure. Their behaviour has been explored by taking advantage of non-linear finite element simulations. The loading conditions included axial compression, transverse compression, pure shear loading, axial compression in combination with transverse compression and axial compression in combination with shear loading. Different patterns of heat affected zones have been studied with particular attention on conventionally welded plates and extruded, welded plates. The plates have been given realistic boundary conditions in addition to boundary conditions believed to represent the extremities in plate collapse behaviour. The initial deflection patterns chosen, were generally conservative, and the variations in collapse capacities for different initial deflection patterns have been investigated. The initial deflection amplitudes were systematically varied to cover all values of the initial deflection amplitudes likely to occur. In addition to studying different patterns of the heat affected zones, systematic variations of the breadths of the heat affected zones have been performed. Systematic variations in the magnitudes of the residual stresses and systematic variations of the reductions of the 0.2 percent tensile proof stresses in the heat affected zones have also been carried out. Three different aluminium alloys were studied. They were believed to represent a high, medium and low utilised aluminium alloy. The aspect ratio of the plates was varied to cover both plates that were completely square to plates with a length equal to five times the breadth of the plates. It was found that axially loaded plates with heat affected zones along loaded edges had lower ultimate capacities than plates with heat affected zones along unloaded edges, and if the plates had heat affected zones along loaded edges, having additional heat affected zones along unloaded edges did not alter the buckling capacities. The reduction in ultimate capacity could be modelled to vary linearly with the breadth of the heat affected zones, and the reduction in ultimate capacity could be modelled to vary linearly with the relationship between the value of the 0.2 percent tensile proof stress in the heat affected zones and the 0.2 percent tensile proof stress of the base material. The ultimate capacities of transversally loaded plates could be found as the sum of a square plate and a plate strip, even if the plates contained heat affected zones. Square plates and plate strips with relevant patterns of heat affected zones had to be employed. Biaxial interaction curves showed a considerable slenderness dependence for all values of the aspect ratio investigated. The biaxial interaction curves were only slightly affected by introduction of different patterns of heat affected zones. The stress corresponding to equal elastic and plastic strain was better suited as the normalising stress than the more commonly used 0.2 percent tensile proof stress. One design curve could be used to represent all the different aluminium alloys investigated. Changing the aluminium alloy did not change the shape of the biaxial interaction curves. Based on the detailed study of the collapse behaviour of aluminium plates carried out, and established practice, new ULS design formulas for axial compression, transverse compression, pure shear loading, axial compression in combination with transverse compression and axial compression in combination with shear loading were proposed. The new design formulas accounted for reductions in ultimate capacities due to heat affected zones, including heat affected zones along loaded edges. They took full advantage of non-linear residual strength for slender plates; and the slenderness dependence and aspect ratio dependence for biaxial interaction curves were systematically incorporated.

The conductive area of a stationary electrical contact consists of many small contact spots. The contact spots can be described as narrow metal bridges across the interface between two conductors. Deterioration of a contact is closely related to processes occurring in these microscopic areas. The objective of this work is to clarify the basic mechanisms affecting the reliability and degradation of an electrical contact by closely studying the contact spots. Particular emphasis has been put on examining the contact spots occurring in aluminium-aluminium interfaces when passing AC. Due to the small thermal capacity of a contact spot the temperature in the contact spot cycles with twice the frequency of the applied AC. The minimum temperature attained during one cycle being the bulk temperature of the conductor, the maximum temperature can in heavily stressed contacts be close to the melting point of the conductor material. In the idealized contact used in the present investigation, this thermal cycling may initiate thermal fatigue processes in the contact spot region. Microscopic cracks appear in the contact spot region as the result of thermal fatigue processes. The cracks not only lower the mechanical strength of the conductor in close vicinity of the contact spot, they also cause a higher electrical resistivity in these areas. Alloying a tracer metal in one of the electrodes of the contact allows for closer investigation of the crack propagation as it occurred during the experiments. The tracer migrates into the heated contact spot region of the opposite electrode where the cracks constitute a barrier impairing further diffusion into the electrode. Further information on the thermal fatigue processes in the contact spot region is obtained when examining metallographic images of cross sectioned contact spots. Here it can be seen that the repetitive thermal stresses give rise to clearly localized recrystallisation in the contact spot region. Thermal fatigue is a well known failure mechanism in mechanical structures. It has to the authors knowledge not previously been associated with the deterioration of contact spots. However, the mechanical damage in the contact spot region caused by the temperature cycling also has a detrimental effect on the electrical behaviour of the contact. It is therefore suggested that thermal fatigue is of considerable importance to the reliability and degradation of stationary electrical contacts.

Following a short introduction, the state-of-the-art fatigue life assessment methods based on the nominal stress, the structural hot spot stress and the effective notch stress, as well as the crack propagation analysis are explained and discussed. Thereafter, the effect of mean stress on crack propagation was investigated by exemplifying crack propagation data from different aluminium alloys. In this context, Walker's equation received wide attention. In addition, a new, simple equation to express the mean stress dependency of crack propagation data has been proposed. In order to generate crack propagation data for the 6082-T6 aluminium alloy, investigate the behaviour of short cracks and find the mean stress dependency of crack growth in this alloy, crack propagation tests of sub-millimetre cracks subjected to different stress ratios have been carried out. The crack depth was successfully monitored on-line employing a special direct current potential drop technique. The crack propagation data generated verified the long crack propagation data given in Eurocode 9. In addition, useful experience was gained to improve future tests. Some evidence was found of accelerated crack growth near the threshold. Based on the data obtained and literature data a Walker exponent γ= 0.78 has been calculated for the aluminium alloy 6082-T6. The fatigue life of welded aluminium T-joints has been estimated using the approaches introduced in Chapter 2. The results have been compared with experimental data from T-joints subjected to 4-point bending. In addition, a series of T-joints subjected to transverse bending has been fatigue tested and the results have been compared with predictions using the same fatigue life assessment methods. The nominal stress gave a conservative prediction in case of the 4-point bending loading. Since no applicable detail category for the transverse bending load case exists, a suitable detail category has been suggested. The structural hot spot stress approach resulted in conservative predictions (factor 4-10 in life) for both load cases. The predictions from the effective notch stress approach are in excellent agreement with the experimental results, where the method using a 1 mm weld toe radius gave the best results. It has been shown that the method can be successfully applied to joints with wall thicknesses down to 3 mm. The fatigue life predicted with the crack propagation approaches is in excellent agreement with the experimental results from the 4-point bending load when the Mk factor was used. Applying the local stress distribution, the predictions are conservative for both load cases. The slopes of all predicted S-N curves, especially from the stress based methods, are steeper than the experimental curves.

This thesis work is the study of the effect of an aluminium foil on the losses that produced by a radiator, situated under a window, through the wall behind it. The reason behind this topic is due to the energy problem and the different goals that governments have set up to try to reduce the use of energy. For example, more specifically a Swedish national goal is to decrease the energy use of the built stock with 50% by 2050.   For this purpose, an experimental set-up was built in the University of Gävle, Sweden. The arrangement was composed by a radiator and a window facing a climate chamber. A total of twenty-one temperatures and two heat fluxes in the exterior wall were measured in the set-up. Ten different measurement scenarios with different radiator temperature, 40°C, 50°C and 60°C; two different distance between the radiator and the wall, 5 and 9 centimetres and with and without the aluminium foil, were performed.   With the experimental results, a CFD model was validated. Two different models were done, first a 2D model and afterwards a 3D model. For the turbulence, the chosen model was standard k-ε model. There were 54 cases simulated with the 2D model and the 3D model was used just for validation. The cases had different variables such as radiator temperature, outdoor temperature and wall insulation. With these cases, analysis of the effectiveness of the presence of an aluminium foil behind the radiator is performed to evaluate if there is a significant reduction of the losses.   The results showed with both methods that the aluminium foil reduces the losses of the wall behind the radiator. The savings varied depending on the boundary conditions of the case and it were obtained a maximum of 4% and a minimum of 1,3%.

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Thèse de doctorat : Électrochimie : Paris 12 : 2006. / Version électronique uniquement consultable au sein de l'Université Paris 12 (Intranet). Titre provenant de l'écran-titre. Bibliogr. : 110 réf.

Thèse de doctorat : sciences. Génie des matériaux : Ecully, Ecole centrale de Lyon : 2005. / 62 réf.

Thèse de doctorat : sciences. Génie des matériaux : Ecully, Ecole centrale de Lyon : 2005. / Titre provenant de l'écran-titre. 62 réf.

Reproduction de : Thèse de doctorat : Science et génie des matériaux : Toulouse, INPT : 2007. / Titre provenant de l'écran-titre. Bibliogr. 104 réf.

Reproduction de : Thèse de doctorat : Sciences de la matière : Toulouse 3 : 2007. / Titre provenant de l'écran-titre. Bibliogr. à la fin des chapitres.