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Deformation Twinning and Grain Size Aspects of Numerical Simulations of Plastic Flow

Published online by Cambridge University Press:  15 February 2011

Frank J. Zerilli  and
Ronald W. Armstrong
Frank J. Zerilli
Affiliation:
Naval Surface Warfare Center, Silver Spring, MD 20903-5640 Supported in part by NSWC Independent Research Funds
Ronald W. Armstrong
Affiliation:
University of Maryland, College Park, MD 20742
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Abstract

The dependence of the twinning stress on grain size is similar to the dependence of the athermal part of the flow stress on grain size. Previous numerical simulations included a twinning effect based upon the premise that twinning refines the grain size and gives additional Hall-Petch strengthening. If a grain reaches the stress level given by σT = σT0+ kT ∓-1/2, it is considered twinned and a constant increment is added to the flow stress. Once twinned, the new twinning threshold stress is much higher than the original and so further twinning is unlikely to occur. The twinning model used in this work is based on the idea that enough twinning will occur in a grain to accommodate the excess by which the Von Mises equivalent stress exceeds the twinning threshold stress. The previous twinning model required knowledge of the number of twins per grain produced. With this model, the parameters for iron are known a priori (σT0 = 330 MPa and kT = 2.8 MPa m1/2) and numerical simulations of Taylor cylinder impacts produced good agreement with experimental results. For titanium and zirconium, σT0 and kT were determined by matching the computed and experimental shapes. The results here indicate that twinning hardens these metals by effectively changing the material grain size and the microstructure within the grains.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 362: Symposium J – Grain-Size and Mechanical Properties--Fundamentals and Applications , 1994 , 149
Copyright
Copyright © Materials Research Society 1995

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References

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