scholarly journals Thermal Activation and Ductile vs. Brittle Behavior of Microcracks in 3D BCC Iron Crystals under Biaxial Loading by Atomistic Simulations

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1525
Author(s):  
Alena Uhnáková ◽  
Anna Machová ◽  
Petr Hora
Keyword(s):  
Elevated Temperature ◽  
Thermal Activation ◽  
Biaxial Loading ◽  
Simple Procedure ◽  
Md Simulations ◽  
Crack Plane ◽  
Dislocation Emission ◽  
Dislocation Generation ◽  
Brittle Behavior ◽  
Microcrack Growth

We present the results of free 3D molecular dynamics (MD) simulations, focused on the influence of temperature on the ductile-brittle behavior of a pre-existing central Griffith through microcrack (1¯10)[110] (crack plane/crack front) under biaxial loading σA and σB in tension mode I. At temperatures of 300 K and 600 K, the MD results provide new information on the threshold values of the stress intensity factor K and the energy release rate G, needed for the emission of <111>{112} blunting dislocations that support crack stability. A simple procedure for the evaluation of thermal activation from MD results is proposed in the paper. 3D atomistic results are compared with continuum predictions on thermal activation of the crack induced dislocation generation. At elevated temperature T and biaxiality ratios σB/σA ≤ 0.8 dislocation emission in MD is observed, supported by thermal activation energy of about ~30 kBT. With increasing temperature, the ductile-brittle transition moves to a higher biaxiality ratios in comparison with the situation at temperature of ~0 K. Near the transition, dislocation emission occurs at lower loadings than expected by continuum predictions. For the ratios σB/σA ≥ 1, the elevated temperature facilitates (surprisingly) the microcrack growth below Griffith level.

Atomistic Study of Cleavage and Dislocation Emission in NiAl

1994 ◽  
Vol 364 ◽  
Author(s):  
M. Ludwig ◽  
P. Gumbsch
Keyword(s):  
Finite Element ◽  
Mixed Mode ◽  
Crack Tip ◽  
Mode I ◽  
Crack Plane ◽  
Dislocation Emission ◽  
Dislocation Generation ◽  
Embedded Atom ◽  
Atomistic Study ◽  
Eam Potential

AbstractThe atomistic processes during fracture of NiAl are studied using a new embedded atom (EAM) potential to describe the region near the crack tip. To provide the atomistically modeled crack tip region with realistic boundary conditions, a coupled finite element - atomistic (FEAt) technique [1] is employed. In agreement with experimental observations, perfectly brittle cleavage is observed for the (110) crack plane. In contrast, cracks on the (100) plane either follow a zig-zag path on (110) planes, or emit dislocations. Dislocation generation is studied in more detail under mixed mode I/II loading conditions.

Crack Orientation versus Ductile-Brittle Behavior in 3D Atomistic Simulations

2007 ◽  
Vol 567-568 ◽  
pp. 61-64 ◽  
Author(s):  
Alena Spielmannová ◽  
Anna Machová ◽  
Petr Hora
Keyword(s):  
Room Temperature ◽  
Md Simulations ◽  
Atomistic Simulations ◽  
Mode I ◽  
Crack Plane ◽  
Crack Orientation ◽  
Brittle Behavior ◽  
Bcc Iron ◽  
Fracture Tests ◽  
Recent Fracture

The paper presents results of molecular dynamic (MD) simulations in 3D bcc iron crystals with edge pre-existing cracks (001)[110] and (110) [110] (crack plane/crack front) loaded uni-axially in tension mode I at temperature of 300 K. The iron crystals in MD have the same orientation and similar geometry as in our recent fracture tests performed at room temperature on iron (3wt.%Si) single crystals [1].

The biaxial loading response of powder aluminum at elevated temperature

1994 ◽  
Vol 34 (3) ◽  
pp. 249-255 ◽  
Author(s):  
T. O. Woods ◽  
D. G. Berghaus
Keyword(s):  
Elevated Temperature ◽  
Biaxial Loading

Size dependence and stochastic nature of yield strength of micron-sized crystals: a case study on Ni 3 Al

2006 ◽  
Vol 462 (2070) ◽  
pp. 1661-1681 ◽  
Author(s):  
A.H.W Ngan ◽  
L Zuo ◽  
P.C Wo
Keyword(s):  
Strong Dependence ◽  
Md Simulations ◽  
Al Alloy ◽  
Dislocation Generation ◽  
Embedded Atom ◽  
Incipient Plasticity ◽  
Material Volume ◽  
General Material ◽  
Atom Potential

Recent experiments indicate that the first yield point of micron-sized metals exhibits significant statistical scatter as well as strong dependence on the specimen size. In this work, molecular dynamics (MD) simulations are carried out to investigate the onset of shear deformation in a small block of material, using an embedded atom potential for the intermetallic Ni 3 Al alloy. Incipient plasticity in the form of homogeneous dislocation generation is observed to occur at atomic sites with interatomic displacements approaching one-half of the Shockley partial Burgers vector. From the distribution function of the interatomic displacements observed in the MD simulations, the probability of a general material volume surviving under given loading conditions is predicted. The survival probability is then calculated for several situations, including homogeneous deformation and nanoindentation, to predict the critical load for incipient plasticity to occur in these situations. The predicted results are compared to micro-pillar compression and nanoindentation experiments on Ni 3 Al available in the literature.

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.

A quantitative criterion for predicting solid-state disordering during biaxial, high strain rate deformation

2021 ◽  
Author(s):  
Michael Becker ◽  
Desiderio Kovar
Keyword(s):  
Stress State ◽  
Strain Rate ◽  
Strain State ◽  
Biaxial Loading ◽  
High Strain ◽  
Md Simulations ◽  
Strain Rates ◽  
Critical Strain Rate ◽  
Wide Range ◽  
High Strain Rate Deformation

Abstract A criterion to predict the onset of disordering under biaxial loading based on a critical potential energy per atom was studied. In contrast to previous theories for disordering, this criterion incorporates the effects of strain rate and strain state. The strain state (or stress state) is defined by the combination of strain (or stress) magnitudes and directions that are applied to each sample during the simulation. Τhe validity of this criterion was studied using molecular dynamic (MD) simulations of Ag conducted over a wide range of biaxial strain rates, strain configurations, and crystal orientations with respect to the applied stress state. Biaxial strains were applied in two different planes, (112 ̅) and (001) in eight directions in each plane. Results showed that, when larger strain rates were applied, there was a transition from plastic deformation driven by the nucleation and propagation of dislocations to disordering and viscous flow. Although the critical strain rate to initiate disorder was found to vary in the range of ε ̇ = 1×1011 s-1 to ε ̇ = 4×1011 s-1, a consistent minimum PE/atom of -2.7 eV was observed over a broad range of strain states and for both crystallographic orientations that were studied. This indicates that the critical PE/atom is a material property that can be used to predict the onset of disordering under biaxial loading. Further, the results showed that this criterion can be applied successfully even when non-uninform strain states arise in the crystal.  

Ductile-Brittle Behavior of Microcracks in 3D

2005 ◽  
Vol 482 ◽  
pp. 131-134
Author(s):  
V. Pelikán ◽  
Petr Hora ◽  
Anna Machová ◽  
Michal Landa
Keyword(s):  
Molecular Dynamics ◽  
Crack Initiation ◽  
Mode I ◽  
Dislocation Emission ◽  
Brittle Behavior ◽  
Free Sample ◽  
Bcc Iron ◽  
Parallel Molecular Dynamics

Results of several parallel molecular dynamics crack simulations in bcc iron crystals with up to 128 million atoms are presented. The crack (001)[010] of Griffith type is loaded in Mode I. We observe dislocation emission and twinning near the free sample surfaces and later plastically induced crack initiation.

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