Dislocation Interaction Embrittlement

Let us return to the reduction of shear stress at the crack tip due to the emission of dislocations. Figure 14-9 illustrates a possible stress reduction mechanism. It can be seen that the tip of a crack is no longer atomically sharp after a dislocation has been emitted. It is the interaction of the external stress field with that of the newly formed dislocations which creates the local stress responsible for further crack growth. Thus, the plastic deformation normally impedes embrittlement because the dislocations screen the crack from the external stress. Theoretical calculations are difficult because the lattice distortions of both tension and shear near the crack tip are large so that nonlinear behavior is expected. In addition, surface effects have to be included. 

A. Munier, R. Schaller, O. Mercier and W.B. Waeber, Interactions of defects with dislocations in reactor pressure vessel steels . Radiation Embrittlement of Reactor Pressure Vessel Steels An International Review (Fourth Volume), ASTM STP1170, L.E. Steele, ed., American Society for Testing and Materials, Philadelphia, PA, 1993,269-282. 

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