The discrete dislocation (DD) plasticity is truly mechanism-based plasticity and well-suited for mesoscale modeling in metal. The effects of size-dependent plasticity and plastic dissipation emerge naturally from this framework.<br/> The micromechanics of fracture is material dependent and involves a broad range of length and time scales. The intermediate situation between the cleavage crack growth and the plastic dissipation involved in fracture based on DD plasticity is focused here.<br/> Fracture crack growth is affected by dislocations: (i) dislocation motion shields the crack tip and increases the dissipation energy and (ii) the local stress concentration associated with discrete dislocation in the vicinity of the crack tip can reach atomic bond strength, causing the crack to grow.<br/> In this work fatigue crack growth from small cracked particle into single crystal is first investigated with a focus on the effects of plastic confinement due to elastic particle, and elastic modulus mismatch between the reinforcement and matrix phases.<br/> The results show that fatigue crack growth from micron-scale particles is strongly influenced by size effect of plasticity, elastic mismatch, and the presence of particle to plastic flow.<br/> However the yield stress of the matrix material and the cohesive strength in the cohesive zone model are unrealistic due to the limitations of the standard DD algorithm.<br/> Also the computational cost and storage can be reduced by using symmetric boundaries.<br/> Therefore the new algorithm of discrete dislocation plasticity to improve the computational efficiency and its application in the short crack problem are presented here.<br/> To study the role of plastic anisotropy on crack growth in a single crystal, the standard DD formulation can be extended to perform the effects of plastic dissipation and dislocation/crack interaction on the basal cleavage in HCP-like material.<br/> To do so, the concept of plastic flow controlled by a Peierls stress is first implemented to the standard DD methodology. The results show that the fracture toughness is largely independent of plastic anisotropy.<br/> Interestingly, the fracture toughnesses of both Peierls stress-controlled flow material and obstacle-controlled flow material are unified through the new Stress Gradient Plasticity concept.
Olarnrithinun, Sutee,
"Discrete Dislocation Modeling of Fracture/Fatigue"
(2013).
Mechanics of Solids Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.7301/Z07W69JC
