Deformation mechanism map

A deformation mechanism map is a way of representing the dominant deformation mechanism in a material loaded under a given set of conditions and thereby its likely failure mode. Deformation mechanism maps consist of some kind of stress plotted against some kind of temperature axis, typically stress normalised using the shear modulus versus homologous temperature.^[1] For a given set of operating conditions calculations are undergone and experiments performed to determine the predominant mechanism operative for a given material.

Constructing the Map

Repeated experiments are performed to characterize the mechanism by which the material deforms. The dominant mechanism is the one by which the material will fail, however at any given level of stress and temperature, more than one of the creep and plasticity mechanisms may be active. It is left to scientific experiment to determine which controls the failure of the material.

Reading the Map

For a given stress profile and temperature, the point lies in a particular "deformation field". If the values place the point near the center of a field, it is likely that the primary mechanism by which the material will fail, i.e.: the type and rate of failure expected, grain boundary diffusion, plasticity, nabarro-herring creep, etc... If however, the stress and temperature conditions place the point near the boundary between two deformation mechanism regions then the dominating mechanism is less clear. Near the boundary there are likely more than one effect that are of sufficient magnitude to affect the deformation and possible failure of the material. Deformation mechanism maps are only as accurate as the number of experiments and calculations undertaken in their creation.

Example: Creep

Creep, a mode of material failure which often requires experimental evidence to construct empirical models of its behavior, is often represented by a deformation mechanism map^[2]. Data from measurements at various levels of stress and temperature are plotted, often with constant strain rate contours included. The map may then be useful to predict one of temperature, stress, and creep strain rate, given the other two.

See also

• continuum mechanics

References

1. ^ Ashby, M.A. (1983). "Mechanisms of Deformation and Fracture". In Hutchinson J.W. & Wu T.Yl. Advances in applied mechanics, Volume 23. Academic Press. pp. 118–179. ISBN 0-12-002023-8. http://books.google.co.uk/books?id=bWI92I53ew8C&pg=PA136&dq=application+%22deformation+mechanism+map%22&lr=&ei=-o7wSuDpJZ-GygTK28jTBw#v=onepage&q=application%20%22deformation%20mechanism%20map%22&f=false. Retrieved 2009-11-03. 
2. ^ Fundamentals of Materials Science and Engineering, William D. Callister, John Wiley and Sons, 2nd International edition (September 3, 2004), ISBN-10: 0471660817, ISBN-13: 978-0471660811, p.334