A SUPERDISLOCATION MODEL FOR THE STRENGTHENING OF METAL-MATRIX COMPOSITES AND THE INITIATION AND PROPAGATION OF SHEAR BANDS

Strengthening in metallic alloys resulting from dislocation-particle i nteraction is investigated in connection with the initiation and propa gation of shear bands. A dislocation model is presented in this work t o explain these phenomena. It consists of a discontinuous tilt wall in itially containing N infinite straight dislocations. The wall interact s with rigid particles and bows out between them as these particles ac t as pinning points. At a critical stress, the bow-out becomes unstabl e and its front propagates to form a shear band. An analytical solutio n is formulated for the increase in the elastic strain energy as the t ilt wall bows out between the two rigid particles. The bow-out configu ration is approximated by a finite number of straight line segments. T he critical state at the onset of instability is obtained by minimizin g the free energy, leading to an estimate for the flow stress and its dependence on particle spacing. The model is in good agreement with ex perimental data found in the literature.