49 research outputs found
Atomistic Studies of Defect Nucleation during Nanoindentation of Au (001)
Atomistic studies are carried out to investigate the formation and evolution
of defects during nanoindentation of a gold crystal. The results in this
theoretical study complement the experimental investigations [J. D. Kiely and
J. E. Houston, Phys. Rev. B, v57, 12588 (1998)] extremely well. The defects are
produced by a three step mechanism involving nucleation, glide and reaction of
Shockley partials on the {111} slip planes noncoplanar with the indented
surface. We have observed that slip is in the directions along which the
resolved shear stress has reached the critical value of approximately 2 GPa.
The first yield occurs when the shear stresses reach this critical value on all
the {111} planes involved in the formation of the defect. The phenomenon of
strain hardening is observed due to the sessile stair-rods produced by the
zipping of the partials. The dislocation locks produced during the second yield
give rise to permanent deformation after retraction.Comment: 11 pages, 13 figures, submitted to Physical Review
Estimation of dislocation densities in cold rolled Al-Mg-Cu-Mn alloys by combination of yield strength data, EBSD and strength models
Al-Mg-Cu-Mn alloys have been developed for the packaging industry, in which large cold-working deformations are normally applied that can produce high dislocation densities. In this study, we present a simplified model for the yield strength contributions and apply that to obtain the dislocation densities by determining the orientation factors, which can be obtained via the crystal information of electron backscatter diffraction (EBSD). One alloy subjected to three cold-rolling reductions (10%, 40% and 90%) has been analysed by EBSD, and the density of dislocations are estimated using the strengthening model. This assessment suggests that dislocation densities by the Taylor model are roughly consistent but slightly lower than those determined by transmission electron microscopy