Ce travail de thèse contribue à étudier le comportement élasto-plastique au rayage du verre métallique massif Zr55Cu30Al10Ni5 par la méthode des éléments finis (MEF) et expérimentaux. Le critère de plasticité de type Drucker-Prager est utilisé, une méthode de remaillage est proposée afin d'éviter le problème de convergence qui vient de la grand contrainte cisaillement. Pour cela, le comportement au rayage est étudié par le changement de l'angle d'attaque, du coefficient de frottement local entre le matériau et l'indenteur. Ces influences sont valorisés par l'évolution des forces rayures, par la morphologie de l'échantillon, et ils montrent le mécanisme de changement des modes de rayage : du labourage à l'usinage avec la formation des copeaux. Les essais sont réalisés à l'aide de l'équipement du LARMAUR : Un nano-triboindenteur de type Hysitron Ti-950. La comparaison des résultats simulés et expérimentaux nous permettre d'évaluer la loi comportement utilisé et d'estimer la valeur de coefficient de frottement entre le matériau et l'indenteur. / This thesis contributes to modeling of the elasto-plastic behavior in scratch test of a Zr55Cu30Al10Ni5 Bulk Metallic Glasses (BMG) by the finite element method and by experimental testing. The Drucker-Prager criterion is used and dedicated re-meshing method is proposed in order to solve the numerical problems classically encountered when modeling such a test and this with a controlled element population. The influence of friction coefficient as well as the angle of attack are investigated to understand the occurrence of two deformation mechanisms : plowing and cutting. The test is realized by using the LARMAUR's equipment : nano triboindenter Hysitron Ti-950. The result of experimental and simulation are confronted the finite element simulations.

Seeking to quench airliners’ unending thirst for lightweight, reliable and more comfortable seating solutions, designers are developing a new generation of slim economy – class seats. Challenge in front of the designers is to carve out additional “living space”, as well as to give a “lie – flat” experience to air travellers with strict adherence to safety regulations. Present research tries to address all these industry needs through an innovative and novel “Sleep Seat”. A generous angle of recline (40 degree), movement of “Seat Pan” along the gradient, fixed outer shell of backrest, and unique single “Forward Beam” design distinguishes “Sleep Seat” form current generation seats. It is an ultralightweight design weighing 8kg (typical seat weight is 11kg). It satisfies “Generic Requirements (GR2)” which ensures “Comfort in Air”. It will be a “16g” seat, means it can sustain the “Emergency landing” loads as specified by “Certification Specifications (CS 25.561 and CS 25.562)”. For present research, only CS 25.561 has been considered. Since, the design of “Sleep Seat” is still in its conceptual phase, it is not possible to build the prototypes and their physical testing, due to costs and time involved. “Finite Element Analysis (FEA)” is a useful tool to predict the response of the structure when subjected to real life loads. Hence, the aim of research being undertaken is to develop a detailed FE model of the complete seat structure, which will help designers to identify potential weak areas and to compare different design concepts virtually, thereby reducing the development cycle time. In order to avoid handling of large number of design variables; major load carrying members (called Primary Load Path) i.e. Forward beam and leg; are designed for the most critical “Forward 9g” loads; using FEA results as a basis. A robust framework to verify the FEA results is developed. “Sequential Model Development Approach”; which builds the final, detailed FE model starting from preliminary model (by continuously updating the FE model by addition of details that are backed up by pilot studies); resulted in a FE model which could predict the stress induced in each of the components for applied CS 25.561 loads along with “Seat Interface Loads”. The “Interface Load” is the force exerted by the seat design on the floor and is one of the main contributing factors in seat design. “Optistruct” is used as a solver for linear static FEA, whereas “Abaqus / Standard” is used for non-linear FEA. Stepwise methodologies for mesh sensitivity study, modelling of bolt-preload, representing bolted joint in FEA, preventing rigid body motion, and obtaining a converged solution for non-linear FEA are developed during this research. Free-Shape Optimisation is used to arrive at a final design of Seat-leg. All the findings and steps taken during this are well documented in this report. Finally, a detailed FE model (involving all the three non-linearities : Contact, material and geometric) of the complete seat structure was analysed for the loads taken from CS 25.561, and it was found that design of “Forward beam” and leg are safe against CS 25.561. Therefore, all the aims and objectives outlined for this research were accomplished. For future work, first area to look for, would be validation of present FEA results by experimental testing. FE model to simulate dynamic loads CS 25.562 can be developed followed by design improvements and optimisation.

After the collapse of the roof structure in Tarfalahallen 2020, great attention has been focused on instability of sub-tensioned glulam roof trusses. Investigations were launched to find the reason for the collapse and the cause was instability in the roof truss that supported the roof. As a result, several similar glulam roof trusses in Sweden have been investigated and reinforced to avoid the fate of Tarfalahallen.Inexperience with instability, negligent design procedure and faulty assumptions is an underlying issue with this type of structure. Complex structures can be difficult to analyze without suitable assumptions which means sophisticated method must be used. Proper analysis must be done before construction.To perform this sophisticated analysis, an engineer can use the finite element method to perform global stability analysis. Simple and computationally cheap models can produce meaningful insight, but in most cases the user must be experienced to understand the implications of the results that the finite element method can produce. There is therefore a need for a more detailed, realistic model that can capture failure and motion and visualize it for the user. This thesis has created such a model in the FE-software Abaqus/Standard.By using a wide variety of elements and element sizes a detailed geometry of the connection between primary beam and compression stud, the behavior of the structural components has been analyzed throughout the loading period of the structure. The critical buckling mode was identified, and the complex non-linear interaction of the connection was tracked when buckling occurs.The thesis can be used as a guideline of how to create a FE-model that captures the intricate behavior of the connection between primary beam and compression stud and be used as the groundwork for more complex models in the future.

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