Strain gradient crystal plasticity: Intergranular microstructure formation

Özdemir, İzzet
Yalçınkaya, Tuncay
This chapter addresses the formation and evolution of inhomogeneous plastic deformation field between grains in polycrystalline metals by focusing on continuum scale modeling of dislocation-grain boundary interactions within a strain gradient crystal plasticity (SGCP) framework. Thermodynamically consistent extension of a particular strain gradient plasticity model, addressed previously (see also, e.g., Yalcinkaya et al, J Mech Phys Solids 59:1-17, 2011), is presented which incorporates the effect of grain boundaries on plastic slip evolution explicitly. Among various choices, a potential-type non-dissipative grain boundary description in terms of grain boundary Burgers tensor (see, e.g., Gurtin, J Mech Phys Solids 56:640-662, 2008) is preferred since this is the essential descriptor to capture both the misorientation and grain boundary orientation effects. A mixed finite element formulation is used to discretize the problem in which both displacements and plastic slips are considered as primary variables. For the treatment of grain boundaries within the solution algorithm, an interface element is formulated. The capabilities of the framework is demonstrated through 3D bicrystal and polycrystal examples, and potential extensions and currently pursued multi-scale modeling efforts are briefly discussed in the closure.


Micromechanical Modelling of Size Effects in Microforming
Yalçınkaya, Tuncay; SIMONOVSKI, IGOR; ÖZDEMİR, İZZET (2017-09-01)
This paper deals with the micromechanical modelling of the size dependent mechanical response of polycrystalline metallic materials at micron scale through a strain gradient crystal plasticity framework. The model is implemented into a Finite Element software as a coupled implicit user element subroutine where the plastic slip and displacement fields are taken as global variables. Uniaxial tensile tests are conducted for microstructures having different number of grains with random orientations in plane str...
Strain gradient crystal plasticity: thermodynamics and implementation
Yalçınkaya, Tuncay (Springer, 2016-01-01)
This chapter studies the thermodynamical consistency and the finite element implementation aspects of a rate-dependent nonlocal (strain gradient) crystal plasticity model, which is used to address the modeling of the size-dependent behavior of polycrystalline metallic materials. The possibilities and required updates for the simulation of dislocation microstructure evolution, grain boundary-dislocation interaction mechanisms, and localization leading to necking and fracture phenomena are shortly discussed a...
Inter-granular Microstructure Formation and Evolution Through Crystal Plasticity
Yalçınkaya, Tuncay (2016-07-24)
Deformation of polycrystalline materials induce intra–granular, inter–granular and trans–granular deformation localization which results in spatially heterogeneous strain and stress distribution affecting the plasticity, damage and fracture of the material. Inter–granular localization is the most common mechanism considering the grain boundaries are natural locations triggering accumulation of the plastic slip and the geometrically necessary dislocations which accommodate the gradients of the inhomogeneous ...
Strain effects on the behavior of isolated and paired sulfur vacancy defects in monolayer MoS2
Sensoy, Mehmet Gokhan; Vinichenko, Dmitry; Chen, Wei; Friend, Cynthia M.; Kaxiras, Efthimios (2017-01-17)
We investigate the behavior of sulfur vacancy defects, the most abundant type of intrinsic defect in monolayer MoS2, using first-principles calculations based on density functional theory. We consider the dependence of the isolated defect formation energy on the charge state and on uniaxial tensile and compressive strain up to 5%. We also consider the possibility of defect clustering by examining the formation energies of pairs of vacancies at various relative positions, and their dependence on charge state...
Intrinsic and Statistical Size Effects in Microforming
Yalçınkaya, Tuncay; Simonovski, Igor; ÖZDEMİR, İZZET (2017-04-28)
This paper analyzes the intrinsic (grain size dependent) and the statistical (grain number and orientation distribution dependent) size effects of micron level polycrystalline metallic specimens under plastic deformation through a strain gradient crystal plasticity framework. The macroscopic and local behavior of specimens from very limited number of grains to high number of grains are studied and the results are discussed in detail taking into account different boundary conditions.
Citation Formats
İ. Özdemir and T. Yalçınkaya, Strain gradient crystal plasticity: Intergranular microstructure formation. 2016, p. 1063.