A Discrete Dislocation Analysis of Crack Growth under Cyclic Loading

1999 ◽  
Vol 578 ◽  
Author(s):  
H.H.M. Cleveringa ◽  
E. Van Der Giessen ◽  
A. Needleman
Keyword(s):  
Stress Intensity ◽  
Cyclic Loading ◽  
Crack Growth ◽  
Elastic Solid ◽  
Dislocation Nucleation ◽  
Dislocation Dynamics ◽  
Small Scale ◽  
Loading Conditions ◽  
Dislocation Interaction ◽  
Discrete Dislocation

AbstractCyclic loading of a plane strain mode I crack under small scale yielding is analyzed using discrete dislocation dynamics. The dislocations are all of edge character, and are modeled as line singularities in an elastic solid. At each stage of loading, superposition is used to represent the solution in terms of solutions for edge dislocations in a half-space and a nonsingular complementary solution that enforces the boundary conditions, which is obtained from a linear elastic, finite element solution. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation are incorporated into the formulation through a set of constitutive rules. An elastic relation between the opening traction and the displacement jump across a cohesive surface ahead of the initial crack tip is also specified, which permits crack initiation and crack growth to emerge naturally. It is found that crack growth can occur under cyclic loading conditions even when the peak stress intensity factor is smaller than the stress intensity required for crack growth under monotonic loading conditions.

Discrete Dislocations Interacting with a Mode I Crack

1998 ◽  
Vol 538 ◽  
Author(s):  
H.H.M. Cleveringa ◽  
E. Van Der Giessen ◽  
A. Needleman
Keyword(s):  
Crack Growth ◽  
Dislocation Motion ◽  
Initial Crack ◽  
Dislocation Nucleation ◽  
Dislocation Dynamics ◽  
Small Scale ◽  
Mode I ◽  
Mode I Crack ◽  
Dislocation Interaction ◽  
Dislocation Annihilation

AbstractSmall scale yielding around a plane strain mode I crack is analyzed using discrete dislocation dynamics. The dislocations are all of edge character, and are modeled as line singularities in an elastic material. At each stage of loading, superposition is used to represent the solution in terms of solutions for edge dislocations in a half-space and a complementary solution that enforces the boundary conditions. The latter is non-singular and obtained from a linear elastic, finite element solution. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation are incorporated into the formulation through a set of constitutive rules. A relation between the opening traction and the displacement jumps across a cohesive surface ahead of the initial crack tip is also specified, so that crack initiation and crack growth emerge naturally. Material parameters representative of aluminum are employed. Two cases are considered that differ in the strength and density of dislocation obstacles. Results are presented for the evolution of the dislocation structure and the near-tip stress field during the early stages of crack growth.

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.

On the Influence of the Corner Singularity on Kinking Mixed-Mode Crack Propagation

2007 ◽  
Vol 348-349 ◽  
pp. 585-588
Author(s):  
Henning Schütte ◽  
Kianoush Molla-Abbasi
Keyword(s):  
Stress Intensity ◽  
Crack Propagation ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
Mixed Mode ◽  
Small Scale ◽  
Intensity Factors ◽  
Plastic Energy ◽  
Mixed Mode Crack ◽  
The Impact

The aim of the presentation is to highlight the influence of the kink, developing at the beginning of mixed-mode crack growth, on the propagation behavior of the crack. Le et al. [1] have shown that the variational principle of a body containing a crack results in the principle of maximum energy release rate incorporating the stress intensity factors of the kinked crack. Here the influence of the kink and the kinking angle, resulting in a singular field around the corner, on the crack growth is analyzed. The generalized stress intensity factors at the kinks corner are computed with the help of a FEM strategy. The influence of these on the T-stresses and the plastic energy dissipated at the kink is determined using a small scale yielding approach. The impact of these results on mixed-mode crack propagation is discussed.

scholarly journals Fracture Mechanics Approach to Creep Crack Growth in Welded IN738LC Gas Turbine Blades

1991 ◽  
Author(s):  
Wan-P’ng Foo ◽  
Rafael Castillo
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Gas Turbine ◽  
Crack Growth ◽  
Turbine Blades ◽  
Creep Crack Growth ◽  
Crack Tip ◽  
Loading Conditions ◽  
Creep Crack

Microcracks caused by hot cracking or strain age cracking mechanisms are very likely to be discovered in the weld repair zone of precision cast IN738LC gas turbine blades. The possibility of crack propagation under the operating conditions of the gas turbine thereby becomes a crucial issue for gas turbine designers. The creep crack growth rate in air of the hipped and fully heat treated IN738LC was measured at the service temperature experienced by the first stage turbine blade tip. The corresponding growth behaviour was also studied. The creep crack growth rate, da/dt, versus crack tip stress intensity factor, K1, a relation which exhibits the typical primary, secondary and tertiary behaviour, supports the applicability of K1 as an appropriate correlating parameter for the creep crack growth of this Ni-based superalloy under the loading conditions used in this study. Microstructural examination illustrated that the creep crack growth of IN738LC principally takes place by the nucleation, growth, coalescence and link-up of grain boundary microvoids and microcracks. An excellent approximation of the stress intensity factor under service loading conditions in the vicinity of the crack tip was obtained by using the Westinghouse WECAN finite element analysis. It is shown that the crack tip stress intensity factor under normal loading conditions will not be able to drive the transverse through-the-wall-thickness blade tip crack in this study.

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