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Mesoscopic and microscopic aspects of the PSB formation mechanism in fatigued FCC monocrystals
Author(s) -
Blochwitz C.,
Burmeister H.J.,
Kremling U.
Publication year - 1983
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.2170180704
Subject(s) - mesoscopic physics , nucleation , dislocation , strain (injury) , materials science , plasticity , condensed matter physics , annihilation , amplitude , stress (linguistics) , hysteresis , crystallography , composite material , physics , thermodynamics , chemistry , optics , anatomy , quantum mechanics , medicine , linguistics , philosophy
Persistent zones of plastic strain localization (PSBs) can be observed in fatigued fee monocrystals above the “nucleation cycle number” N n and the “nucleation stress” amplitude τ n , respectively. They follow after temporary strain localizations existing at N < N n and being discernible by oscillations of the relative shape of the hysteresis loops ( V H ) or by strain bursts. Using a simple rheological model the frequency of internal stresses of mesoscopic wave length (“mesoscopic stresses”) was determined for Ni monocrystals fatigued at four different plastic strain amplitudes up to N n . A “mesoscopic threshold stress” τ* has been found to be exceeded within the whole volume of the dislocation‐dense regions (DRs) at N ≧ N n . By comparison of τ* with the stress for the operation of Frank‐Read sources of the segment lengths l 0 at the border of the DRs, it might be assumed that above N n and τ n respectively a mechanism of dislocation sources acts, compensating the high annihilation rate of movable dislocations in the zones of strain localization. In so doing the formation of persistent zones of strain localization becomes possible, in which the “ladder‐like” dislocation structure of the final PSBs develops successively.