Fatigue failure is dominated by local mechanisms: strain localization, crack initiation and propagation. Grain boundaries are known for their role in strengthening polycristalline materials but many fracture investigations revealed that fatigue crack initiation frequently occurred from or near grain boundaries, especially in the case of face centered cubic (FCC) materials. In order to characterize an interface behavior and its orientation dependency, a crystal plasticity model was implemented using the finite element method and the behavior of few FCC bicrystalline configurations have been investigated under monotonic loading.
Four criterions have been identified as governing crystal plasticity: the anisotropic elastic modulus, the primary and the secondary system Schmid factors and finally the ratio between the two latter. First, simple monotonic tension simulations of well-defined orientations have permitted to show the effect of each criterion on the single crystal mechanical behavior, in terms of stress-strain curves, progressive slip system activation (plastic hardening), and local crystal rotation. Then, bicrystalline simulations were run and their analysis highlighted a specific elasto-plastic behavior nearby grain boundaries. Particularly, the activation of nonfavored slip systems was noted and is associated with the need of mechanical compatibility across the interface structure. Axial stress and strain profiles have also shown systematic stress maxima near (but not at) the interface and strain minima at the grain boundary. Moreover, the more the strain dropped at the interface, the higher the misorientation between the two crystals increased.
Finally, a particular case where slip trace in grain boundary plan were compatible was investigated in terms of local strain, local stress profiles and slip system activation history. No correlation could be found between the compatibility condition and the mechanical field magnitude. Instead the deformation profile showed the same systematic drop when approaching the grain boundary. Macro-mechanical features such as global rotation, anisotropy and misorientation seemed to be the cause of that drop profile.
| Date | 15 Feb 2013 |
|---|
| Original language | French |
|---|
| Awarding Institution | - École de technologie supérieure
|
|---|
| Supervisor | Philippe Bocher (Supervisor), Florent Bridier (Co-supervisor) & Remi Dingreville (Co-supervisor) |
|---|
Andriamisandratra, M. (Author),
Bocher (Supervisor), Bridier (Co-supervisor) & Dingreville (Co-supervisor),
15 Feb 2013Student thesis: Master's thesis › Master in Engineering: Mechanical Engineering