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 usually consist of some kind of stress plotted against some kind of temperature axis, typically stress normalised using the shear modulus versus homologous temperature with contours of strain rate.[1] [2] For a given set of operating conditions calculations are undergone and experiments performed to determine the predominant mechanism operative for a given material.
Deformation Maps can also be constructed using any two of stress (normalised), temperature (normalised) and strain rate, with contours of the third variable. A stress/strain rate plot is useful because power-law mechanisms then have contours of temperature which are straight lines.
Deformation mechanism Maps should not be confused with the similar but distinct Failure Mechanism maps, which were also first developed by Ashby.
Contents
Constructing the Map
Repeated experiments are performed to characterize the mechanism by which the material deforms. The dominant mechanism is the one which dominates the continuous deformation rate (strain rate), however at any given level of stress and temperature, more than one of the creep and plasticity mechanisms may be active.
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.[3] 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
References
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- ↑ Fundamentals of Materials Science and Engineering, William D. Callister, John Wiley and Sons, 2nd International edition (September 3, 2004), ISBN 0-471-66081-7, ISBN 978-0-471-66081-1, p.334
