How to Measure a Dislocation’s Breakthrough Stress to Estimate the Grain Boundary Resistance against Slip Transfer Based on the DFZ-Model of Fracture

2016 ◽  
Vol 258 ◽  
pp. 93-96 ◽  
Author(s):  
Florian Schaefer ◽  
Matthias Thielen ◽  
Michael Marx ◽  
Christian Motz
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Plastic Zone ◽  
Density Distribution ◽  
Fatigue Cracks ◽  
Local Stress ◽  
Boundary Resistance ◽  
Zone Model ◽  
Free Zone ◽  
Slip Transfer

Stage-I-fatigue-cracks are used as highly localized dislocation sources with well-known Burger’s vectors to study the interaction between dislocations and grain boundaries. This interaction in the plastic zone is of particular interest to understand the fluctuating crack growth in the very short crack regime. In the case of a blocked slip band the dislocations pile up at the grain boundary causing a local stress concentration. The resulting local stress distribution is calculated based on measurements of the dislocation density distribution in the plastic zone. For this purpose the slip line profiles were measured by AFM, the dislocation density distribution was determined and the dislocation-free zone model of fracture (DFZ) was validated. With this it is possible to quantify the grain boundary resistance and to combine geometric and stress approach for grain boundary resistance against slip transfer.

scholarly journals Detection of grain-boundary resistance to slip transfer using nanoindentation

2005 ◽  
Vol 59 (24-25) ◽  
pp. 3192-3195 ◽  
Author(s):  
W.A. Soer ◽  
J.Th.M. De Hosson
Keyword(s):  
Grain Boundary ◽  
Boundary Resistance ◽  
Slip Transfer

Dislocation emission criterion: Grain boundary effect

1993 ◽  
Vol 8 (8) ◽  
pp. 1853-1857 ◽  
Author(s):  
Sham-Tsong Shiue ◽  
Tong-Yi Zhang ◽  
Sanboh Lee
Keyword(s):  
Grain Size ◽  
Stress Intensity ◽  
Grain Boundary ◽  
Plastic Zone ◽  
Critical Stress ◽  
Boundary Effect ◽  
Critical Stress Intensity Factor ◽  
Dislocation Emission ◽  
Brittle Behavior ◽  
Free Zone

Based on the results of Shiue and Lee [J. Appl. Phys. 70, 2947 (1991)], the effect of plastic zone and grain boundary on the dislocation emission criterion was investigated. The emission criterion is based on the concept of spontaneous emission. The critical stress intensity factor for dislocation emission increases with the increasing size of dislocation-free zone and the number of piled-up dislocations in the plastic zone, but decreases with increasing grain size. The ductile versus brittle behavior of material was determined by the competition of critical stress intensity factors for dislocation emission and crack propagation. A material with larger grain size is easier to emit dislocation and allows more dislocations to be piled up, so that it behaves more ductile.

scholarly journals MODELING OF NANOINDENTATION AND MICROSTRUCTURAL DUCTILE BEHAVIOR IN METALLIC MATERIAL SYSTEMS

2004 ◽  
Vol 841 ◽  
Author(s):  
Jeong Beom Ma ◽  
W. Ashmawi ◽  
M. A. Zikry ◽  
D. Schall ◽  
D. W. Brenner
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Large Scale ◽  
Dynamic Models ◽  
Local Stress ◽  
Stress Fields ◽  
Metallic Material ◽  
Density Distributions ◽  
Ductile Behavior ◽  
The Continuum

ABSTRACTSpecialized large-scale computational finite-element and molecular dynamic models have been used to understand and predict how dislocation density emission and contact stress fields due to nanoindentation affect inelastic deformation evolution at scales that span the molecular to the continuum level in ductile crystalline systems. Dislocation density distributions and local stress fields have been obtained for different crystalline slip-system and grain-boundary orientations. The interrelated effects of grain-boundary interfaces and orientations, dislocation density evolution and crystalline structure on indentation inelastic regions have been investigated.

scholarly journals Creep-Fatigue Crack Initiation Simulation of a Modified 12% Cr Steel Based on Grain Boundary Cavitation and Plastic Slip Accumulation

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6565
Author(s):  
Xin Jin ◽  
Run-Zi Wang ◽  
Yang Shu ◽  
Jia-Wen Fei ◽  
Jian-Feng Wen ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Grain Boundary ◽  
Power Plants ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Local Stress ◽  
Average Grain Size ◽  
Creep Fatigue ◽  
Creep Fatigue Crack

High-temperature components in power plants may fail due to creep and fatigue. Creep damage is usually accompanied by the nucleation, growth, and coalescence of grain boundary cavities, while fatigue damage is caused by excessive accumulated plastic deformation due to the local stress concentration. This paper proposes a multiscale numerical framework combining the crystal plastic frame with the meso-damage mechanisms. Not only can it better describe the deformation mechanism dominated by creep from a microscopic viewpoint, but also reflects the local damage of materials caused by irreversible microstructure changes in the process of creep-fatigue deformation to some extent. In this paper, the creep-fatigue crack initiation analysis of a modified 12%Cr steel (X12CrMoWvNBN10-1-1) is carried out for a given notch specimen. It is found that creep cracks usually initiate at the triple grain boundary junctions or at the grain boundaries approximately perpendicular to the loading direction, while fatigue cracks always initiate from the notch surface where stress is concentrated. In addition to this, the crack initiation life can be quantitatively described, which is affected by the average grain size, initial notch size, stress range and holding time.

scholarly journals Dislocation density distribution at slip band-grain boundary intersections

2020 ◽  
Vol 182 ◽  
pp. 172-183 ◽  
Author(s):  
Yi Guo ◽  
David M. Collins ◽  
Edmund Tarleton ◽  
Felix Hofmann ◽  
Angus J. Wilkinson ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Density Distribution ◽  
Slip Band ◽  
Boundary Intersections

Observations of dislocation interactions with recrystallized grain boundaries

1988 ◽  
Vol 46 ◽  
pp. 628-629
Author(s):  
C. W. Price
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Dislocation Structure ◽  
Hot Deformation ◽  
Static Recrystallization ◽  
High Dislocation Density ◽  
High Angle ◽  
Dislocation Interactions

Little evidence exists on the interaction of individual dislocations with recrystallized grain boundaries, primarily because of the severely overlapping contrast of the high dislocation density usually present during recrystallization. Interesting evidence of such interaction, Fig. 1, was discovered during examination of some old work on the hot deformation of Al-4.64 Cu. The specimen was deformed in a programmable thermomechanical instrument at 527 C and a strain rate of 25 cm/cm/s to a strain of 0.7. Static recrystallization occurred during a post anneal of 23 s also at 527 C. The figure shows evidence of dissociation of a subboundary at an intersection with a recrystallized high-angle grain boundary. At least one set of dislocations appears to be out of contrast in Fig. 1, and a grainboundary precipitate also is visible. Unfortunately, only subgrain sizes were of interest at the time the micrograph was recorded, and no attempt was made to analyze the dislocation structure.

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