Simulation of Hot Sheet Metal Forming Processes Based on a Micro-Structural Constitutive Model

2011 ◽  
Vol 473 ◽  
pp. 556-563 ◽  
Author(s):  
Mahmoud Farzin ◽  
Reza Jafari Nedoushan ◽  
Mohammad Mashayekhi
Keyword(s):  
Experimental Data ◽  
Grain Boundary ◽  
Constitutive Model ◽  
Strain Rate ◽  
Boundary Diffusion ◽  
Grain Boundary Sliding ◽  
Grain Boundary Diffusion ◽  
Hot Forming ◽  
Proposed Model ◽  
Boundary Sliding

A constitutive model is proposed for simulations of hot forming processes. Dominant mechanisms in hot forming including inter-granular deformation, grain boundary sliding and grain boundary diffusion are considered in the constitutive model. A Taylor type polycrystalline model is used to predict inter-granular deformation. Previous works on grain boundary sliding and grain boundary diffusion are extended to drive three dimensional macro stress-strain rate relationships for each mechanism. In these relationships, the effect of grain size is also taken into account. It is shown that for grain boundary diffusion, stress-strain rate relationship obeys the Prandtl-Reuss flow rule. The proposed model is used to simulate step strain rate tests and the results are compared with experimental data. It is concluded that the model can be used to predict flow stress for various grain sizes and strain rates. The proposed model can be directly used in simulation of hot forming processes and as an example the bulge forming process is simulated and the results are compared with experimental data.

Simulation of Super-Plastic Forming Based on a Micro-Structural Constitutive Model and Considering Grain Growth

2011 ◽  
Vol 473 ◽  
pp. 610-617 ◽  
Author(s):  
Mahmoud Farzin ◽  
Reza Jafari Nedoushan ◽  
Mohammad Mashayekhi
Keyword(s):  
Grain Boundary ◽  
Constitutive Model ◽  
Grain Growth ◽  
Boundary Diffusion ◽  
Constitutive Models ◽  
Yield Function ◽  
Grain Boundary Sliding ◽  
Grain Boundary Diffusion ◽  
Simple Tension ◽  
Boundary Sliding

Constitutive models based on dominant mechanisms in hot forming are proposed. These models consider inter-granular deformation, grain boundary sliding, grain boundary diffusion and grain growth. New stress-strain rate relationships are proposed to predict deformation due to grain boundary sliding and grain boundary diffusion. Beside a Taylor type polycrystalline constitutive model, a visco-plastic relation in conjunction with a yield function is used to predict inter-granular deformation with much less computational costs. The proposed models are calibrated with tensile test data of AA5083 at . The calibrated models closely fit simple tension experimental data for various strain rates and strains. Then as an example the models are used to simulate a tray forming experiment. Dome heights and tray thicknesses at various positions during forming time can well predict experimental observations.

A Model for the Effects of Strain Rate and Temperature on the Deformation Behavior of Ultrafine-Grained Metals

2011 ◽  
Vol 291-294 ◽  
pp. 1173-1177
Author(s):  
Zi Ling Xie ◽  
Lin Zhu Sun ◽  
Fang Yang
Keyword(s):  
Grain Boundary ◽  
Strain Rate ◽  
Deformation Behavior ◽  
Boundary Diffusion ◽  
Rate Sensitivity ◽  
Grain Boundary Sliding ◽  
Dislocation Slip ◽  
Deformation Response ◽  
Ultrafine Grained ◽  
Boundary Sliding

A theoretical model is developed to account for the effects of strain rate and temperature on the deformation behavior of ultrafine-grained fcc Cu. Three mechanisms, including dislocation slip, grain boundary diffusion, and grain boundary sliding are considered to contribute to the deformation response simultaneously. Numerical simulations show that the strain rate sensitivity increases with decreasing grain size and strain rate, and that the flow stress and tensile ductility increase with either increasing strain rate or decreasing deformation temperature.

Analysis of Creep Deformation Due to Grain-Boundary Diffusion/Sliding

2007 ◽  
Vol 345-346 ◽  
pp. 565-568
Author(s):  
Byung Nam Kim ◽  
Keijiro Hiraga ◽  
Koji Morita ◽  
Hidehiro Yoshida
Keyword(s):  
Grain Size ◽  
Creep Rate ◽  
Grain Boundary ◽  
Boundary Diffusion ◽  
Effective Diffusion ◽  
High Viscosity ◽  
Grain Boundary Sliding ◽  
Grain Boundary Diffusion ◽  
Grain Sizes ◽  
Boundary Sliding

For steady-state deformation caused by grain-boundary diffusion and viscous grain-boundary sliding, the creep rate of regular polyhedral grains is analyzed by the energy-balance method. For the microstructure, the grain-grain interaction increases the degree of symmetry of diffusional field, resulting in a decrease of the effective diffusion distance. Meanwhile, the viscous grain-boundary sliding is found to decrease the creep rate. The present analysis reveals that the grain-size exponent is dependent on the grain size and the grain-boundary viscosity: the exponent becomes unity for small grain sizes and/or high viscosity, while it is three for large grain sizes and/or low viscosity.

scholarly journals Stress concentrations, diffusionally accommodated grain boundary sliding and the viscoelasticity of polycrystals

2010 ◽  
Vol 467 (2130) ◽  
pp. 1624-1644 ◽  
Author(s):  
L. C. Lee ◽  
S. J. S. Morris ◽  
J. Wilkening
Keyword(s):  
Stress Field ◽  
Grain Boundary ◽  
Boundary Diffusion ◽  
Finite Thickness ◽  
Grain Boundary Sliding ◽  
Grain Boundary Diffusion ◽  
Interfacial Region ◽  
Stress Concentrations ◽  
Boundary Sliding ◽  
Time Periodic

Using analytical and numerical methods, we analyse the Raj–Ashby bicrystal model of diffusionally accommodated grain-boundary sliding for finite interface slopes. Two perfectly elastic layers of finite thickness are separated by a given fixed spatially periodic interface. Dissipation occurs by time-periodic shearing of the viscous interfacial region, and by time-periodic grain-boundary diffusion. Although two time scales govern these processes, of particular interest is the characteristic time t D for grain-boundary diffusion to occur over distances of order of the grain size. For seismic frequencies ωt D ≫1, we find that the spectrum of mechanical loss Q −1 is controlled by the local stress field near corners. For a simple piecewise linear interface having identical corners, this localization leads to a simple asymptotic form for the loss spectrum: for ωt D ≫1, Q −1 ∼const. ω − α . The positive exponent α is determined by the structure of the stress field near the corners, but depends both on the angle subtended by the corner and on the orientation of the interface; the value of α for a sawtooth interface having 120 ° angles differs from that for a truncated sawtooth interface whose corners subtend the same 120 ° angle. When corners on an interface are not all identical, the behaviour is even more complex. Our analysis suggests that the loss spectrum of a finely grained solid results from volume averaging of the dissipation occurring in the neighbourhood of a randomly oriented three-dimensional network of grain boundaries and edges.

scholarly journals Grain boundary sliding associated with low strain rate at 1000 °C in recrystallized ODS ferritic steel

2016 ◽  
Vol 9 ◽  
pp. 338-341 ◽  
Author(s):  
R. Kamikawa ◽  
S. Ukai ◽  
N. Oono ◽  
T. Kaito ◽  
T. Torimaru ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Strain Rate ◽  
Ferritic Steel ◽  
Grain Boundary Sliding ◽  
Boundary Sliding ◽  
Low Strain Rate
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