7. Conclusion

The elastic theory of dislocations is a relevant basis for the study of plasticity as long as we limit ourselves to the geometric and static aspects of deformation phenomena: study of the plastic deformation mode, existence of internal stresses (plastic deformation incompatibility, elastic interactions between immobile defects). The analysis of internal stresses, combined with that of thermal activation, provides a semi-quantitative description of a large number of mechanical behaviors. However, there are a number of important phenomena that cannot be described when the evolution of the substructure has to be taken into account. These include instability phenomena, or atypical behaviors such as Ni ₃ Al or Be deformed in prismatic slip. The underlying reason for this is that plastic deformation is an essentially dynamic phenomenon.