In this study, the conventional Bailey-Hirsch’s relationship is extended in order to express
the increase of critical resolved shear stress due to the lack of dislocation lines in a grain. This model
is introduced into a triple-scale crystal plasticity model based on geometrically necessary crystal
defects and the homogenization method. A FE simulation is carried out based on the proposed model
for FCC polycrystals with different grain sizes. It is numerically predicted that yield behavior of
fine-grained metals depends on the initial dislocation density and the initial grain size. Furthermore,
yield point drop that is observed in annealed FCC fine-grained metal can be reproduced.
In this paper , a triple − sca 】 e crystal plastic 重 ty nlodel bridging three hierarchical lnateriai str しlc . tures , 正 . e , , dislocatiQn structure , grain aggregate and practical macroscopic s 亡ructure is devclopcd , Geometrically necessary ( GN ) dislocation density and GN incompatibility are employed so as tQ describe isolated dislocations and dislocation pairs in a grain , respectively . Then the homogenization rnethod is hユtroduced into the GN dislocation − cTystal plasticity model for derivation of 亡 he governillg equatiQn of macroscopic structure w { tb the mathematical and physical c { msistencies . Using the prcscnt Inodel , a triple − scale FE simulation briclging the abc )ve tllree hierarchical structures is carried out for f . c . c , polycrystals with djffere 飢 mean grain size . It is shown that the present model can qualitatively reproduce size effects of Inacroscopic specimen with u 畫 trafine grain , i ・ e ・ , the i1 ユerease Qf initial yield stress , the decrease of hardening ratiQ after reachil19 且 e τ lsile strellgth alld the reductioll of tensile ducUlity with decrease of its grain size . MQreQver, the relationship between macroscopic yielding of specimen and microscopic grain yielding is discussed and the mechanism of the poor tcnsile ductility due to 且ne graining is clarified
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