The bending of marble

The arrangement of the dislocations has been studied in iron in various conditions, namely annealed, cold-worked, recovered and after creep. In all conditions the dislocation network is characterized by attractive intersections where two dislocations join to make one dislocation, and there is convincing evidence for the idea that at many of these intersections two $\frac{1}{2}$a$\langle111\rangle$ dislocations join to make one a$\langle100\rangle$ dislocation. These attractive intersections are thought to contribute substantially to the flow stress. These are also repulsive intersections but according to calculation they constitute weaker obstacles to flow than the attractive junctions.