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Amplitude Equation for a Dynamic Strain Aging Model: Beyond Linear Stability Analysis of Serrated Flow in Metallic Alloys

Published online by Cambridge University Press:  21 March 2011

Sergey N. Rashkeev
Affiliation:
Dept. of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA
Michael V. Glazov
Affiliation:
Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069-0001, USA
Frédéric Barlat
Affiliation:
Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069-0001, USA
Daniel J. Lege
Affiliation:
Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069-0001, USA
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Abstract

A method for construction of “processing windows” to avoid negative strain rate sensitivity and associated serrated flow in some aluminum alloys is described. The method is based on the amplitude Ginzburg-Landau (GL) equations and analysis of bifurcation diagrams. The mathematical technique developed in the present work was applied to a specific aluminum alloy, Al-0.4%Mg-0.2%Si considered earlier in the literature [1-3], and yielded good results in terms of predicting the negative strain rate sensitivity regions in the “strain rate “temperature” parameter space. Using the GL-analysis it was demonstrated that even though the instability area is located in the region of intermediate strain rates, a qualitative difference exists between the areas of (relatively) fast and (relatively) slow strain rates. In the first case the dynamic behavior of the system is supercritical, in the second case it is subcritical. The second case is highly undesirable because it causes a sudden onset of stable stress serrations that are difficult to suppress, while in the first case the development of instability is gradual and, consequently, more easily controllable.

Type
Research Article
Copyright
Copyright © Materials Research Society 2001

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