scholarly journals Strain gradient crystal plasticity modelling of size effects in a hierarchical martensitic steel using the Voronoi tessellation method

2019 ◽  
Vol 119 ◽  
pp. 215-229 ◽  
Author(s):  
Fengwei Sun ◽  
Edward D. Meade ◽  
Noel P. O'Dowd
Keyword(s):  
Crystal Plasticity ◽  
Strain Gradient ◽  
Size Effects ◽  
Martensitic Steel ◽  
Voronoi Tessellation

Simulation of Torsion of Thin FCC Single Crystal Wires by Mechanism-Based Strain Gradient Crystal Plasticity

2014 ◽  
Vol 626 ◽  
pp. 139-144 ◽  
Author(s):  
Yi Ping Chen ◽  
Ying Ying Cai ◽  
Q. Ni ◽  
G.Y. Zhao
Keyword(s):  
Single Crystal ◽  
Crystal Plasticity ◽  
Strain Gradient ◽  
Size Effects ◽  
Surface Strain ◽  
Slip Resistance ◽  
User Material Subroutine ◽  
Different Diameters ◽  
The Relationship ◽  
Active Slip

The size effects observed in the torsion of thin FCC single crystal wires is modelled by the employment of mechanism-based strain gradient crystal plasticity (MSG-CP). In the formulation the total slip resistance in each active slip system is assumed to be due to a mixed population of forest obstacles arising from both statistically stored and geometrically necessary dislocations. The MSG-CP constitutive model is implemented into the Abaqus/Standard FE platform by developing the User MATerial subroutine UMAT. By implementing the formulation, the relationship between the non-dimensional torque and the surface strain of the thin copper single crystal wires of different diameters is obtained with the [001] direction along that of the wire axis. The simulation results of torsion reveal size effects, which is in a qualitative agreement with those reported in existing literatures. An appreciable axial elongation is also found in the torsion of single crystal wires.Key words Size effect, MSG-CP model, Torsion

Scale-Dependent Crack Modeling for Investigation the Effect of Geometrically Necessary Dislocations in Micro/Nano Grain Size of Copper

2016 ◽  
Vol 15 ◽  
pp. 1-16 ◽  
Author(s):  
Amin Zaami ◽  
Ali Shokuhfar
Keyword(s):  
Grain Size ◽  
Stress Concentration ◽  
Strain Gradient ◽  
Stress Concentration Factor ◽  
Size Effects ◽  
Crack Tip ◽  
Length Scale ◽  
State Variables ◽  
Dependent Model ◽  
Homogeneous Strain

In this study, a scale-dependent model is employed to investigate the size effects of copper on the behavior of the crack-tip. This model includes the homogeneous and non-homogeneous strain hardening based on the wavelet interpretation of size effect. Introducing additional micro/nano structural considerations together with decreasing grain size, different size effects can be obtained. As the size dependency is not taken into account in conventional plasticity, an enhanced theory which is related to the strain gradient introduces a length scale will give more realistic representations of state variables near the crack-tip. Accordingly, the contribution of geometrically necessary dislocations (GNDs) activity on strengthening and stress concentration factor is identified in the crack-tip. Finally, the affected zone which is dominated by presence of GNDs is identified

Evolution of Crystal Orientations in Plastically Deformed Steels: Role of Constitutive Models Used in Finite Element Simulations

2013 ◽  
Author(s):  
Samir El Shawish ◽  
Leon Cizelj ◽  
Igor Simonovski
Keyword(s):  
Finite Element ◽  
Stainless Steel ◽  
Plastic Strain ◽  
Crystal Plasticity ◽  
Power Plants ◽  
Voronoi Tessellation ◽  
Finite Element Simulations ◽  
Plasticity Model ◽  
Crystal Orientations ◽  
Individual Grains

Stainless steel is a commonly used material in safety-important components of nuclear power plants. In order to study degradation mechanisms in stainless steels, like crack initiation and propagation, it is important to characterize the degree of plastic strain on microstructural level. One way to estimate local plastic strain is by measuring local crystal orientations of the scanned surfaces: the electron backscatter diffraction (EBSD) measurements on stainless steel revealed a strong correlation between the spread of crystal orientations within the individual grains and the imposed macroscopic plastic strain. Similar behavior was also reproduced by finite element simulations where stainless steel was modeled by an anisotropic elasto-plastic constitutive model. In that model the anisotropic Hill’s plasticity function for yield criteria was used and calibrated against the EBSD measurements and macroscopic tensile curve. In this work the Hill’s phenomenological model is upgraded to a more sophisticated crystal plasticity model where plastic deformation is assumed to be a sum of crystalline slips in all activated slip systems. The hardening laws of Peirce, Asaro and Needleman and of Bassani and Wu are applied in crystal plasticity theory and implemented numerically within the user subroutine in ABAQUS. The corresponding material parameters are taken from literature for 316L stainless steel. Finite element simulations are conducted on the analytical Voronoi tessellation with 100 grains and initial random crystallographic orientations. From the simulations, crystal and modified crystal deformation parameters are calculated, which quantify mean and median spread of crystal orientations within individual grains with respect to central grain orientation. The results are compared to EBSD measurements and previous simulations performed with Hill’s plasticity model.

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