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.

An atomic model of crack tip deformation in aluminum using an embedded atom potential

1990 ◽  
Vol 5 (2) ◽  
pp. 313-324 ◽  
Author(s):  
R. G. Hoagland ◽  
M. S. Daw ◽  
S. M. Foiles ◽  
M. I. Baskes
Keyword(s):  
Crack Tip ◽  
Atomic Displacement ◽  
Crack Plane ◽  
Dislocation Emission ◽  
Displacement Fields ◽  
Linear Elastic ◽  
Embedded Atom ◽  
Equilibrium Configurations ◽  
Field Dislocation ◽  
Atom Potential

The atomic configuration at the tip of a mode 1 crack in aluminum is modeled by means of molecular dynamics calculations using an embedded atom potential. This potential intrinsically incorporates many-body contributions. This paper is concerned with the characteristics of the atomic displacement fields in comparison to the linear elastic predictions and dislocation emission phenomena. Three crack/crystal orientations are examined in which the crack plane–crack propagation directions are (010)-[100], (10)-[110], and (10)-[111]. The first two models behaved in a brittle fashion as dislocation emission did not occur for reasons associated with the use of periodic boundary conditions parallel to the crack front. For the models which remained atomically sharp, the positions of the atoms near the crack tip in equilibrium configurations are different from the linear elastic predictions but, to first order, retain an r1/2 dependence, with smaller K, and with the origin displaced behind the physical crack tip. This near tip region is also observed to be elastically softer than in the far field. Dislocation emission readily proceeds in the (10)-[111] model by the sequential emission of partials with attendant nonzero uz displacements. The blunting is characterized by the creation of two corner defects that separate as emission occurs and relaxation of the strains in the region initially confronted by the crack tip. Additional features of the results are discussed.

scholarly journals Numerical Estimation of Notch Stress Intensity Factors of Sharp V-Notches

2018 ◽  
Vol 172 ◽  
pp. 03001
Author(s):  
Mirzaul Karim Hussain ◽  
K.S.R.K. Murthy
Keyword(s):  
Finite Element ◽  
Present Method ◽  
Mixed Mode ◽  
Least Squares Method ◽  
Mode I ◽  
Intensity Factors ◽  
Notch Stress ◽  
Stress Components ◽  
Mode Stress ◽  
Notch Stress Intensity Factors

In the present work a simple and efficient least squares method is implemented for accurate estimation of notch stress intensity factors (NSIFs) of sharp V-notches. Finite element (FE) stress components near a notch tip is used in the present method for determining the NSIFs. Pure mode I and mixed mode (I/II) examples are considered for numerical investigations. The mixed mode stress components are disintegrated into opening mode and shear mode stress components to separate out the mode I and mode II singularities. Thereafter, least squares method is implemented to calculate mixed mode NSIFs. The present method is easy to incorporate in existing standard finite element codes. The results obtained by the present method are found to be in good agreement with the published data.

A Novel Singular Finite Element on Mixed-Mode Dugdale Model Based Crack

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
W. A. Yao ◽  
X. F. Hu
Keyword(s):  
Finite Element ◽  
Analytical Solutions ◽  
Mixed Mode ◽  
Crack Tip ◽  
Dugdale Model ◽  
Dual Approach ◽  
Singular Finite Element ◽  
Crack Tip Opening ◽  
Method Show ◽  
Dugdale Crack

The symplectic dual approach is employed to obtain the analytical solutions of displacements and stresses around the mixed-mode Dugdale crack tip. Based on the analytical solutions, a novel singular finite element is developed to study the problem. The singular finite element can be applied to determine the sizes of crack tip opening/sliding displacement of a mixed-mode Dugdale model. Numerical results obtained by the present method show excellent agreement with the existing analytical solutions.

scholarly journals Analysis of Inclined Cracks in Thin-Walled Circular Tube under Mixed-Mode I + II Fracture

Proceedings ◽  
2018 ◽  
Vol 2 (8) ◽  
pp. 517 ◽  
Author(s):  
Boy Raymond Mabuza
Keyword(s):  
Fracture Mechanics ◽  
Mixed Mode ◽  
Crack Tip ◽  
Theoretical Models ◽  
Mode I ◽  
Mixed Mode Fracture ◽  
Shear Stresses ◽  
Inclined Crack ◽  
Mode Fracture ◽  
Thin Walled

This paper provides a study on mixed-mode fracture mechanics in thin-walled tube which is subjected to tension, shear and torsion loading. This type of loading causes an inclined crack to develop and generate a mixture of normal and shear stresses ahead of a crack tip. The stress state ahead of a crack tip is frequently based on mixed-mode type of interactions which designate the amplitude of the crack tip stresses. The analytical expressions for the stress intensity factors for mixed-mode I + II approach are presented. The Paris law for mixed-modes I + II has been discussed. Mixed-mode fracture mechanics is used with theoretical models to predict the path of crack growth when an inclined crack is subjected to a combination of mode I and mode II deformations. The torque at which crack propagation can be expected has been determined. The numerical calculations have been carried out by using MATLAB code. The results are good and could be useful for companies working with thin-walled circular tubes.

Comparison of mixed mode fracture criteria in finite element analysis for matrix crack density estimation of laminated composites

2020 ◽  
Vol 55 (2) ◽  
pp. 277-289
Author(s):  
Mingqing Yuan ◽  
Haitao Zhao ◽  
Li Tian ◽  
Boming Zhang ◽  
Yanzhi Yang ◽  
...  
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Density Estimation ◽  
Mixed Mode ◽  
Crack Density ◽  
Mode I ◽  
Mixed Mode Fracture ◽  
Fracture Criteria ◽  
Element Analysis ◽  
Mode Fracture

A mixed mode crack density estimation method based on the finite element analysis (FEA) for laminated composites is proposed and verified in this paper. The damaged properties of cracked ply are obtained using semi-analytical micro-mechanical method for the first time. The piecewise functions of the mode I and mode II energy release rates involving crack density are given based on Griffith’s energy principle and discrete damage mechanics (DDM). Any mixed mode fracture criteria could be simply applied to the FEA of the structure to calculate the initiation and evolution of the micro-cracks in the laminate. Mode I criterion, power law and B-K criterion are applied in the numerical examples to compare their performances in the crack density estimation. It has been concluded that the accuracy of the fracture toughness is more important than the choice of fracture criterion in crack density estimation.

scholarly journals Crack Growth and Energy Release Rate for an Angled Crack under Mixed Mode Loading

2020 ◽  
Vol 10 (12) ◽  
pp. 4227
Author(s):  
Yali Yang ◽  
Seok Jae Chu ◽  
Wei song Huang ◽  
Hao Chen
Keyword(s):  
Energy Release Rate ◽  
Numerical Method ◽  
Energy Release ◽  
Release Rate ◽  
Mixed Mode ◽  
Crack Tip ◽  
Theoretical Expression ◽  
Propagation Mechanism ◽  
Mode I ◽  
Theoretical Derivation

The evaluation of energy release rate with angle is still a challenging task in metal crack propagation analysis, especially for the mixed Mode I-II-III loading situation. In this paper, the energy release rate associated with stress intensity factors at an arbitrary angle under mixed mode loadings has been investigated using both a numerical method and theoretical derivation. A relatively simple and precise numerical method was established through a series of spatial-inclined ellipses in Mode I-II and ellipsoids in Mode I-II-III, with different propagation angles computed from simulation. Meanwhile, a theoretical expression of the energy release rate with angle for a crack tip under a I-II-III mixed mode crack was deduced based on the propagation mechanism of the crack tip under the influence of a stress field. It is confirmed that the theoretical expression deduced could provide results as accurately as the present numerical method. The present results were confirmed to be effective and accurate by comparison with experimental data and other literature.

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