On non-glide stresses and their influence on the screw dislocation core in body-centred cubic metals I. The Peierls stress

1984 ◽  
Vol 392 (1802) ◽  
pp. 145-173 ◽  
Keyword(s):  
Screw Dislocation ◽  
Applied Stress ◽  
Strong Dependence ◽  
Dislocation Core ◽  
Peierls Stress ◽  
Exact Nature ◽  
Theoretical Shear Strength ◽  
Stress Variation ◽  
Cubic Model ◽  
Model Lattice

The response of the screw dislocation core in a body-centred cubic model lattice to a general applied stress tensor is examined by means of computer simulation. The Peierls stress is found to have the symmetry required by Neumann’s principle but is found also to have a very strong dependence on shear components of the applied stress which should not interact with the screw dislocation. Rather than having the constant value suggested by the Schmid law of critical resolved shear stress, the Peierls stress can vary from zero to the theoretical shear strength of the lattice, depending upon the exact nature of the critical applied stress components. Calculations with different interatomic binding potentials show that the Peierls stress variation, while different in detail, remains broadly the same, suggesting an origin in the dislocation core geometry rather than the specific charac­teristics of the force laws. Specialization to the case of uniaxial applied stress shows that the similar Peierls stress variation can nevertheless lead to quite different orientation dependences of the flow stress in different materials. Applications to the problem of brittle fracture and possible sources of the Peierls stress variation are discussed briefly.

On non-glide stresses and their influence on the screw dislocation core in body-centred cubic metals. II. The core structure

1984 ◽  
Vol 392 (1802) ◽  
pp. 175-197 ◽  
Keyword(s):  
Stress Tensor ◽  
Screw Dislocation ◽  
Applied Stress ◽  
Elastic Strain ◽  
Elastic Anisotropy ◽  
Dislocation Core ◽  
Core Structure ◽  
Peierls Stress ◽  
The Core ◽  
Anisotropic Elastic

The change in core structure of the screw dislocation in a body-centred cubic lattice subjected to a general applied stress tensor is studied by means of computer simulation. The large variations observed are found not to be correlated with the applied stress, in that the same deformed core structure can be realized by many different combinations of stress components. Instead, the core structure is found to be characterized almost exclusively by the magnitude and orientation of the induced glide strain, with a much smaller dependence on the glide stress. This means that while the force acting on a dislocation is defined by the applied stress, it is the elastic strain within the lattice that determines the resistance to motion. This explains the anomalously large dependence of the Peierls stress upon non-glide components of the applied stress tensor. The Peierls stress varies strongly with the shape of the dislocation core, which depends upon the glide strain. However, the glide strain is in turn dependent on non-glide components of the applied stress by way of anisotropic elastic couplings. Therefore the Peierls stress is itself dependent on the non-glide stresses, to an extent governed by the elastic anisotropy. The possible origin of the strain-dependence of the core structure in elastic strain multiplet forces (equal and opposite generalized forces acting on the dislocation) is discussed briefly, as are implications for the phenomenon of ductile fracture.

Core energy and Peierls stress of a screw dislocation in bcc molybdenum: A periodic-cell tight-binding study

2004 ◽  
Vol 70 (10) ◽  
Author(s):  
Ju Li ◽  
Cai-Zhuang Wang ◽  
Jin-Peng Chang ◽  
Wei Cai ◽  
Vasily V. Bulatov ◽  
...  
Keyword(s):  
Screw Dislocation ◽  
Tight Binding ◽  
Binding Study ◽  
Peierls Stress ◽  
Periodic Cell ◽  
Core Energy

scholarly journals First-Principles Calculations of Oxygen-Dislocation Interaction in Magnesium

Materials ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 116
Author(s):  
Chao Fang ◽  
Jing Zhang ◽  
Ying Huang ◽  
Jianhao Chen
Keyword(s):  
Screw Dislocation ◽  
First Principles ◽  
Dislocation Core ◽  
Prismatic Slip ◽  
Interstitial Oxygen ◽  
First Principles Calculations ◽  
Dislocation Interaction ◽  
Dislocation Glide ◽  
Deformation Behaviors ◽  
Oxygen Atoms

The interaction between interstitial oxygen atoms and <a>-type screw dislocations was investigated via first-principles calculations to elucidate the effect of oxygen solutes on the deformation behaviors of Mg. The results show that repulsive interactions exist between basal screw dislocation cores and oxygen atoms, which would enable the full basal dislocation to bypass the oxygen atoms in the dislocation glide plane through the cross-slip process. This repulsion also increases the resistance to the motion of dissociated basal dislocations. Moreover, the energy of prismatic <a>-type screw dislocation cores is reduced by the presence of oxygen, which would stabilize the screw dislocation core on the prismatic plane, accordingly facilitating the prismatic slip. This information can complement the fundamental knowledge of alloying Mg using interstitial solutes.

Simple Flexible Boundary Conditions for the Atomistic Simulation of Dislocation Core Structure and Motion

1992 ◽  
Vol 291 ◽  
Author(s):  
Roberto Pasianot ◽  
Eduardo J. Savino ◽  
Zhao-Yang Xie ◽  
Diana Farkas
Keyword(s):  
Atomistic Simulation ◽  
Dislocation Line ◽  
Dislocation Core ◽  
Dislocation Motion ◽  
Peierls Stress ◽  
Rigid Boundary ◽  
The Past ◽  
Structure And Motion ◽  
Linear Effects ◽  
Dislocation Core Structure

ABSTRACTFlexible boundary codes for the atomistic simulation of dislocations and other defects have been developed in the past mainly by Sinclair [1], Gehlen et al.[2], and Sinclair et al.[3]. These codes permitted the use of smaller atomic arrays than rigid boundary codes, gave descriptions of core non-linear effects and allowed fair assessments of the Peierls stress for dislocation motion. Green functions (continuum or discrete) or surface traction forces were used to relax the boundary atoms.A much simpler approach is followed here. Core and mobility effects at the boundary are accounted for by a dipole tensor centered at the dislocation line, whose components constitute six more parameters of the minimization process. Results are presented for [100] dislocations in NiAl. It is shown that, within the limitations of the technique, reliable values of the Peierls stress are obtained.

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