On Source-Limited Dislocations in Nanoindentation

2004 ◽  
Vol 71 (3) ◽  
pp. 433-435 ◽  
Author(s):  
M. X. Shi ◽  
Y. Huang ◽  
M. Li ◽  
K. C. Hwang
Keyword(s):  
Material Behavior ◽  
Source Distribution ◽  
Dislocation Model ◽  
Dislocation Source ◽  
Dislocation Generation ◽  
Discrete Dislocation

The discrete dislocation model is used in this note to investigate the source-limited dislocation generation and glide in nanoindentation. It is shown that once there are enough sources for dislocation generation, the material behavior becomes independent of the dislocation source distribution.

Equilibrium Configuration of Epitaxially Strained Thin Film Surfaces

1995 ◽  
Vol 399 ◽  
Author(s):  
K. Jagannadham ◽  
J. Narayan ◽  
J.P. Hirth
Keyword(s):  
Strain Relaxation ◽  
Minimum Energy ◽  
Continuous Distribution ◽  
Radius Of Curvature ◽  
Dislocation Model ◽  
Quasi Equilibrium ◽  
Dislocation Generation ◽  
Discrete Dislocation ◽  
Thick Substrate ◽  
Germanium Silicon

ABSTRACTThe formation of convex and concave regions on the surface of a strained thin epitaxial film on a thick substrate is analyzed by minimization of energy associated with the configuration. The strain energy change resulting from the formation of undulations is modelled with the strain in the film represented by a continuous distribution of dislocations along the perturbed surface and the interface. A discrete dislocation model is also used when periodic undulations are formed. Results of energy minimization for germanium or germanium-silicon alloy films on silicon substrate illustrate that convex regions tend to grow. On the other hand, convex regions formed to conserve mass in shape changes associated with concave regions become stable with minimum energy under quasi-equilibrium when the mobility of adatoms is low. We have determined the size and radius of curvature of the undulations at minimum energy and conclude that it is favorable to form atomic steps on the surfaces from which dislocation generation and strain relaxation takes place.

Quantitative Infrared Photoelasticity of Silicon Photovoltaic Wafers Using a Discrete Dislocation Model

2015 ◽  
Vol 82 (1) ◽  
Author(s):  
T.-W. Lin ◽  
G. P. Horn ◽  
H. T. Johnson
Keyword(s):  
Residual Stress ◽  
Numerical Modeling ◽  
Strain Energy ◽  
Dislocation Model ◽  
Slip Systems ◽  
Inspection Method ◽  
Crystalline Defects ◽  
Discrete Dislocation ◽  
Stress Mapping ◽  
And Performance

Residual stress and crystalline defects in silicon wafers can affect solar cell reliability and performance. Infrared photoelastic measurements are performed for stress mapping in monocrystalline silicon photovoltaic (PV) wafers and compared to photoluminescence (PL) measurements. The wafer stresses are then quantified using a discrete dislocation-based numerical modeling approach, which leads to simulated photoelastic images. The model accounts for wafer stress relaxation due to dislocation structures. The wafer strain energy is then analyzed with respect to the orientation of the dislocation structures. The simulation shows that particular locations on the wafer have only limited slip systems that reduce the wafer strain energy. Experimentally observed dislocation structures are consistent with these observations from the analysis, forming the basis for a more quantitative infrared photoelasticity-based inspection method.

A Discrete Dislocation Plasticity Analysis of Plane-Strain Indentation of a Single-Crystal Half-Space by a Smooth and a Rough Rigid Asperity

2010 ◽  
Author(s):  
X. Yin ◽  
K. Komvopoulos
Keyword(s):  
Single Crystal ◽  
Plane Strain ◽  
Half Space ◽  
Crystal Surface ◽  
Normal Load ◽  
Surface Profile ◽  
Dislocation Source ◽  
Discrete Dislocation ◽  
Dislocation Plasticity ◽  
Edge Dislocations

A discrete dislocation plasticity analysis of plane-strain indentation of a single-crystal half-space by a smooth or rough (fractal) rigid asperity is presented. The emission, movement, and annihilation of edge dislocations are incorporated in the analysis through a set of constitutive rules [1,2]. It is shown that the initiation of the first dislocation is controlled by the subsurface Hertzian stress field and occurs in the ±45° direction with respect to the normal of the crystal surface, in agreement with the macroscopic yielding behavior of the indented halfspace. For fixed slip-plane direction, the dislocation density increases with the applied normal load and dislocation source density. The dislocation multiplication behavior at a given load is compared with that generated by a rough indenter with a fractal surface profile. The results of the analysis provide insight into yielding and plastic deformation phenomena in indented single-crystal materials.

A Discrete Dislocation Plasticity Analysis of a Single-Crystal Half-Space Indented by a Rigid Cylinder

2011 ◽  
Vol 78 (4) ◽  
Author(s):  
X. Yin ◽  
K. Komvopoulos
Keyword(s):  
Single Crystal ◽  
Half Space ◽  
Slip Plane ◽  
Coarse Grained ◽  
Material Strength ◽  
Dislocation Source ◽  
Rigid Cylinder ◽  
Source Density ◽  
Discrete Dislocation ◽  
Dislocation Plasticity

Elastic-plastic indentation of a single-crystal half-space by a rigid cylinder was analyzed by discrete dislocation plasticity. Short-range dislocation interactions were modeled by a set of constitutive rules of dislocation emission, glide, pinning (by obstacles), and annihilation. The occurrence of the first dislocation dipole, multiplication of dislocations, and evolution of subsurface stress field were examined in terms of contact load, dislocation source density, slip-plane distance and orientation angle, and indenter radius. In the presence of defects (dislocation sources), the critical load for dislocation initiation is less than that of a defect-free medium and depends on dislocation source density, slip-plane distance, and indenter radius. The critical indenter radius resulting in deformation under the theoretical material strength is determined from numerical results, and the role of dislocation obstacles is interpreted in terms of their spatial density. Simulations provide insight into yielding and plastic deformation of indented single-crystal materials, and establish a basis for developing coarse-grained plasticity models of localized contact deformation in polycrystalline solids.

Continuum Mechanics-Discrete Defect Modeling and Bubble Raft Simulation of Cracked Specimen Response in Nanoscale Geometries

2002 ◽  
Vol 740 ◽  
Author(s):  
Michael J. Starr ◽  
Walter J. Drugan ◽  
Maria d. C. Lopez-Garcia ◽  
Donald S. Stone
Keyword(s):  
Fracture Behavior ◽  
Crack Tip ◽  
Crack Size ◽  
Dislocation Model ◽  
Dislocation Emission ◽  
Crack Location ◽  
Discrete Dislocation ◽  
Emission Behavior ◽  
The Continuum ◽  
Continuum Elasticity

ABSTRACTIn a continuation of prior work, a new group of Bragg bubble model experiments have been performed to explore the effects of nanoscale crack size and nanoscale structural geometry on atomically-sharp crack tip dislocation emission behavior. The experiments have been designed to correspond to the theoretical limits that bound the expected crack tip response. Continuum elasticity analyses of these situations have also been carried out, in which the leading-order terms in the Williams expansion (the K and T terms) are determined, and the predictions of these continuum analyses coupled with discrete dislocation theory are compared with the experimental results. The experiments exhibit fascinating changes in crack tip dislocation emission direction with changing crack and structural size, crack location and loading conditions, as well as substantial changes in the magnitude of the resolved shear stress that drives dislocation emission. These changes are predicted well by the continuum elasticity-discrete dislocation model down to extremely small dimensions, on the order of a few atomic spacings. Preliminary experiments were performed with layered and two-atom basis rafts to establish crucial comparisons between theory and experiment that validate the applicability of continuum elasticity theory to make predictions directly related to nanoscale fracture behavior.

In-Situ TEM Deformation Studies of Dislocation Generation and Motion in High-Purity MO Single Crystals

1999 ◽  
Vol 578 ◽  
Author(s):  
M. Jouiad ◽  
B. W. Lagow ◽  
I. M. Robertson ◽  
D. H. Lassila
Keyword(s):  
Single Crystals ◽  
Screw Dislocation ◽  
High Purity ◽  
In Situ Tem ◽  
Dislocation Source ◽  
Dislocation Generation ◽  
Transmission Electron ◽  
Dislocation Tangle ◽  
Source Operation

AbstractThe generation and motion of dislocations in high-purity single crystals of Mo have been observed in real time by deforming electron-transparent samples in-situ in a transmission electron microscope. At 300 K and at low levels of stress, a novel dislocation source was observed that generated a long, straight screw dislocation. The source was a dislocation tangle that existed in the annealed material. An edge dislocation emerged from the tangle, trailing behind it the screw dislocation. These screw dislocations were immobile at this stress level. At higher stresses, the same dislocation tangle generated many dislocations, but now by a pole mechanism. The nature of these tangles and the source operation mechanisms will be described.

Sign in / Sign up

Export Citation Format

Share Document