Authors: A.A. Kodentsov, M.J.H. van Dal, Csaba Cserháti, Lajos Daróczi, F.J.J. van Loo
73
Authors: George C. Kaschner, Jeffrey C. Gibeling
Abstract: Strain rate jump tests were performed during low cycle fatigue using plastic strain rate as
the real time computed control variable. Test materials included OFE polycrystalline copper,
AA7075-T6 aluminum, and 304 stainless steel. The evolution of dislocation interactions was
observed by evaluating the activation area and true stress as a function of cumulative plastic strain.
Activation area values for each of the three materials were evaluated from an initial state to
saturation. All three materials exhibit a deviation from Cottrell-Stokes law during cyclic
deformation. Tests performed on each of the three materials at saturation reveal a dependence of
activation area on plastic strain amplitude for copper and aluminum but no such relationship for
stainless steel. These results reflect a contrast between wavy slip for pure copper and 7075
aluminum versus planar slip for 304 stainless steel tested at room temperature. Dislocation motion
in copper transitions from forest dislocation cutting [1-6] to increasing contributions of cross slip.
Dislocation motion in 7075 aluminum and 304 stainless steel is controlled by obstacles that are
characteristically more thermal than forest dislocations: obstacles in 7075-T6 aluminum are
identified as solutes from re-dissolved particles; obstacles in 304 stainless steel are also solutes.
371
Authors: Yoshiteru Aoyagi, Naohiro Horibe, Kazuyuki Shizawa
Abstract: In this study, we develop a multiscale crystal plasticity model that represents evolution of
dislocation structure on formation process of ultrafine-grained metal based both on dislocation
patterning and geometrically necessary dislocation accumulation. A computation on the processes of
ultrafine-graining, i.e., generation of dislocation cell and subgrain patterns, evolution of dense
dislocation walls, its transition to micro-bands and lamellar dislocation structure and formation of
subdivision surrounded by high angle boundaries, is performed by use of the present model.
Dislocation patterning depending on activity of slip systems is reproduced introducing slip rate of
each slip system into reaction-diffusion equations governing self-organization of dislocation structure
and increasing immobilizing rate of dislocation with activation of the secondary slip system. In
addition, we investigate the effect of active slip systems to the processes of fine-graining by using the
pseudo-three-dimensional model with twelve slip systems of FCC metal.
1057
Authors: Xiao Chun Ma, Ji Hui Yin
Abstract: The thermal effect has pronounced influence on deformation behavior of materials at nanoscale due to small length scale. In current paper, shear deformation of single crystal copper is simulated by molecular dynamics simulation, and special attention is paid to the thermal effect on the deformation behavior of material and mechanical response. The result shows that the plastic deformation of material during shear deformation is dominated by dislocation activities. Both the yield strength and shear strength have strong dependence on temperature due to thermal effect.
155
Authors: Su Gui Tian, Ben Jiang Qian, Fu Shun Liang, An An Li, Xing Fu Yu
Abstract: By the measurement of creep curves and microstructure observation, an investigation has been made into the creep behaviors and microstructure evolution of a single crystal nickel-based superalloy containing 4.2%Re. Results show that the superalloy displays an obvious sensibility on the applied temperatures and stresses in the range of the applied temperatures and stresses. During the initial creep, the cubical g¢ phase in the alloy is transformed into an N-type rafted structure along the direction vertical to the applied stress axis. After crept up to fracture, the rafted g¢ phase in the region near fracture is transformed into a twisted configuration. The dislocation climbing over the rafted g¢ phase is considered to be the main deformation mechanism of the alloy during the steady creep state, and dislocations shear into the rafted g¢ phase is the main deformation mechanism of the alloy in the later stage of creep.
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