Several precipitate configurations were investigated using an original treatment of precipitate-dislocation interactions and a parallelized dislocation-dynamics code. In grains which contained single-sized shearable particles (rp = 160nm), the strain was localized in clear bands where the precipitates were totally sheared-off. The fatigue behaviour involved an initial hardening followed by severe cyclic softening and significant surface slip irreversibility. In the presence of large single-sized particles (rp = 400nm), the persistent slip band structure was accompanied by highly reversible surface displacements. Slip dispersion originated from Orowan loops that had little effect upon the mechanical response. The mechanical behaviour of a bimodal distribution was intermediate between the above 2 cases with the above microstructural features coexisting within the same grain. Unlike the monomodal large-particle case, where all of the particles retained their initial strength, some of the large particles of the bimodal distribution underwent a significant strength reduction.

Fatigue in Precipitation Hardened Materials - a Three-Dimensional Discrete Dislocation Dynamics Modelling of the Early Cycles. C.S.Shin, C.F.Robertson, M.C.Fivel: Philosophical Magazine, 2007, 87[24], 3657-69