Dislocation Dipole Study on Material Hardening/Softening

Author(s):  
Abu Bakar Siddique ◽  
Tariq Khraishi ◽  
Hojun Lim
Keyword(s):  
Author(s):  
E. L. Thomas ◽  
S. L. Sass

In polyethylene single crystals pairs of black and white lines spaced 700-3,000Å apart, parallel to the [100] and [010] directions, have been identified as microsector boundaries. A microsector is formed when the plane of chain folding changes over a small distance within a polymer crystal. In order for the different types of folds to accommodate at the boundary between the 2 fold domains, a staggering along the chain direction and a rotation of the chains in the plane of the boundary occurs. The black-white contrast from a microsector boundary can be explained in terms of these chain rotations. We demonstrate that microsectors can terminate within the crystal and interpret the observed terminal strain contrast in terms of a screw dislocation dipole model.


Author(s):  
N. Y. Jin

Localised plastic deformation in Persistent Slip Bands(PSBs) is a characteristic feature of fatigue in many materials. The dislocation structure in the PSBs contains regularly spaced dislocation dipole walls occupying a volume fraction of around 10%. The remainder of the specimen, the inactive "matrix", contains dislocation veins at a volume fraction of 50% or more. Walls and veins are both separated by regions in which the dislocation density is lower by some orders of magnitude. Since the PSBs offer favorable sites for the initiation of fatigue cracks, the formation of the PSB wall structure is of great interest. Winter has proposed that PSBs form as the result of a transformation of the matrix structure to a regular wall structure, and that the instability occurs among the broad dipoles near the center of a vein rather than in the hard shell surounding the vein as argued by Kulmann-Wilsdorf.


2017 ◽  
Vol 228 (7) ◽  
pp. 2541-2554 ◽  
Author(s):  
Jianfeng Zhao ◽  
Jinlin Liu ◽  
Guozheng Kang ◽  
Linan An ◽  
Xu Zhang

Author(s):  
Xu Wang ◽  
Peter Schiavone

Using conformal mapping techniques, we design novel lamellar structures which cloak the influence of any one of a screw dislocation dipole, a circular Eshelby inclusion or a concentrated couple. The lamellar structure is composed of two half-planes bonded through a middle coating with a variable thickness within which is located either the dislocation dipole, the circular Eshelby inclusion or the concentrated couple. The Eshelby inclusion undergoes either uniform anti-plane eigenstrains or uniform in-plane volumetric eigenstrains. As a result, the influence of any one of the dislocation dipole, the circular Eshelby inclusion or the concentrated couple is cloaked in that their presence will not disturb the prescribed uniform stress fields in both surrounding half-planes.


2012 ◽  
Vol 67 (1) ◽  
pp. 69-72 ◽  
Author(s):  
H.J. Chu ◽  
J. Wang ◽  
I.J. Beyerlein
Keyword(s):  

2011 ◽  
Vol 33 (10) ◽  
pp. 1369-1375 ◽  
Author(s):  
Steffen Brinckmann ◽  
Rakulan Sivanesapillai ◽  
Alexander Hartmaier

1972 ◽  
Vol 22 (3) ◽  
pp. 189-203 ◽  
Author(s):  
Z. Knésl ◽  
F. Kroupa

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