Atomistic-Dislocation Dynamics Modelling of Fatigue Microstructure and Crack Initiation

2013 ◽  
Author(s):  
Nasr M. Ghoniem
Keyword(s):  
Crack Initiation ◽  
Dislocation Dynamics ◽  
Dynamics Modelling ◽  
Fatigue Microstructure

scholarly journals Analysis of the Crack Initiation and Growth in Crystalline Materials Using Discrete Dislocations and the Modified Kitagawa–Takahashi Diagram

Crystals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 358
Author(s):  
Kuntimaddi Sadananda ◽  
Ilaksh Adlakha ◽  
Kiran N. Solanki ◽  
A.K. Vasudevan
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Growth Kinetics ◽  
Dislocation Dynamics ◽  
Internal Stresses ◽  
Stress Concentrations ◽  
Crystalline Materials ◽  
Discrete Dislocation ◽  
Continuous Crack ◽  
American Society

Crack growth kinetics in crystalline materials is examined both from the point of continuum mechanics and discrete dislocation dynamics. Kinetics ranging from the Griffith crack to continuous elastic-plastic cracks are analyzed. Initiation and propagation of incipient cracks require very high stresses and appropriate stress gradients. These can be obtained either by pre-existing notches, as is done in a typical American Society of Testing and Materials (ASTM) fatigue and fracture tests, or by in situ generated stress concentrations via dislocation pile-ups. Crack growth kinetics are also examined using the modified Kitagawa–Takahashi diagram to show the role of internal stresses and their gradients needed to sustain continuous crack growth. Incipient crack initiation and growth are also examined using discrete dislocation modeling. The analysis is supported by the experimental data available in the literature.

scholarly journals First Steps of Crack Initiation and Propagation in Fatigue of FCC Crystals Studied by Dislocation Dynamics

2012 ◽  
Author(s):  
C. Déprés ◽  
G. V. Prasad Reddy ◽  
L. Tabourot ◽  
R. Sandhya ◽  
S. Sankaran
Keyword(s):  
Stress Field ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Crack Initiation ◽  
Crack Tip ◽  
Dislocation Dynamics ◽  
Crack Initiation And Propagation ◽  
Dislocation Dynamic ◽  
Discrete Dislocation ◽  
Initiation And Propagation

3D discrete dislocation dynamic (DDD) simulations are performed to simulate stage-I fatigue crack initiation and propagation along the surface, in the primary grain and its neighbouring grain, in 316L stainless steel. The scenario of crack propagation in primary grain and the evolution of dislocation structure ahead of crack tip are discussed, and in addition crack tip sliding displacement is estimated. Probable mechanisms of crack propagation from primary grain to neighbouring grain are evaluated. In this process, surface relief in the neighbouring-grain under the influence of crack stress field in the primary grain is studied for varying neighbouring-grain orientations. An enhanced evolution of surface extrusions in the neighbouring grain, are observed in the presence of heterogeneous stress field (i.e., in the presence of crack in the primary grain), compared to that in the case of homogeneous stress field. In addition, influence of crack stress field on prior cyclic-deformed substructure is presented.

The Effect of Mean Stress and Thermo-Mechanical Induced Stress on Micro-Crack Initiation: An Analysis Based on Experiments and DD Simulation Results

2007 ◽  
Vol 567-568 ◽  
pp. 89-92 ◽  
Author(s):  
Christian F. Robertson ◽  
Christophe Déprés ◽  
Marc Fivel
Keyword(s):  
Crack Initiation ◽  
Tensile Loading ◽  
Dislocation Dynamics ◽  
Normal Vector ◽  
304L Stainless Steel ◽  
Mean Stress ◽  
Slip Systems ◽  
Static Tensile Loading ◽  
Static Tensile ◽  
The Individual

The combined effect of cyclic thermal shocks and static tensile loading is investigated, in a 304L stainless steel. During these experiments, the stress state in the cylindrical specimen walls is nearly equi-biaxial (σZZ ≈ σθθ). In dislocation dynamics (DD) simulations carried out with σZZ = σθθ, the predominant slip directions b are nearly aligned with the free surface normal vector n, regardless of their associated activation ratio (A.R.). This effect is related to the "surface connected volume" (SCV) of the predominant slip systems. Hence, surface grains with n = <110> possess "large SCV slip systems" and therefore, constitute preferential sites for micro-crack initiation in thermal fatigue. During the tests, a marked effect of the superimposed static tensile loading (or mean stress) is also noted. This effect is explained with the help of DD simulations performed with a positive mean stress: slip irreversibility in the individual persistent slip bands systematically augments with increasing mean stress.

A method to predict fatigue crack initiation in metals using dislocation dynamics

2017 ◽  
Vol 35 (4-5) ◽  
pp. 325-341 ◽  
Author(s):  
Christian Heinrich ◽  
Veera Sundararaghavan
Keyword(s):  
Fatigue Crack ◽  
Dislocation Density ◽  
Crack Initiation ◽  
Gibbs Energy ◽  
Dislocation Structure ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Dislocation Dynamics ◽  
Continuum Energy ◽  
Number Of Cycles

AbstractA theory is proposed to predict the initiation of fatigue cracks using cyclic dislocation dynamics (DD) simulations. The evolution of dislocation networks in a grain is simulated over several cycles. It is shown that the dislocation density and the energy stored in the dislocation networks increase with the number of cycles. The results of the DD simulations are used to construct an energy balance expression for crack initiation. A hypothetical crack is inserted into the grain, and the Gibbs energy consisting of the energy of the dislocation structure, the surface energy of the hypothetical crack, and the reduction in continuum energy is evaluated. Once the Gibbs energy attains a maximum, the dislocation structure becomes unstable, and it becomes energetically more favorable to form a real crack. The proposed method is applied to oxygen-free high conductivity copper, and the results are compared against experiments. Finally, it is shown how the method can be amended to account for environmental effects.

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