Examinator: Christer Persson, IMS
Opponent: Professor Reinhart Pippan, Austrian Academy of Science, Austria
In their operating environment, metals can undergo a modification of their material properties. In specific cases, the formation of compounds, such as rust, more brittle than the rest of the material, can induce a decrease of the carrying capacities of a metallic structure. Such phenomena combined to the application of a mechanical load can lead to drastic material failures. In nuclear power plant and space rockets, some key structures are exposed to hydrogen, whose interaction with titanium or zirconium-based materials can give rise to hydrogen embrittlement through the formation of brittle hydride.
To prevent dramatic outcomes, the study of such phenomena appears clearly necessary. In order to reduce the costs and possible impacts on the environment, the means of simulation is preferred to experiment. In this thesis, mathematical models and numerical methodologies, based on modern tools, such as phase field theory, linear elastic fracture mechanics and finite element method, are developed and analyzed to investigate the formation of material compounds in metallic structures operating in specific environments and loading conditions. A particular attention is given to the formation of hydride near opening crack tips, areas of high stress concentration. The models and methods presented in this thesis allow to capture many relevant aspects with numerical efficiency.
In the future, the integration of such models and methodologies in commercial software could contribute to the increase of cost and time efficiency of engineering projects.