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Research assistant and PhD position at PoliMi on micro-plasticity models

S. Beretta's picture

In the last decade, different
cyclic plasticity models
, based on the “continuum” approach, have been proposed
in order to account for different mechanical effects (such as ratchetting,
strain range dependence, non-proportional loading and memory effect), [1, 2]. A
disadvantage of this approach is the elevated number of model parameters
introduced in order to correctly predict the material behaviour. The determination
of these parameters, usually difficult and expensive,
is one of the reasons why the modern
constitutive models are not widely used in finite element simulations of
complex fatigue problems.

 

 

An alternative view is to
consider model development based on fundamental mechanisms to represent a wide
range of experimental responses in an acceptable way with fewer model
parameters, [3, 4]. This kind of models are based on a micro–macro transition. The
transition from grain to the slip system level is usually achieved by using the
resolved shear stress. This approach allows to reduce the number of the material
parameters respect to the unified model types. However, until now, some effects
of specific microstructure such as grain neighbourhood, grain size, grain shape
are not yet incorporated, [5].

The
purpose of this
research project is to study different
elasto-plastic single crystal models and to extend their application to
polycrystalline materials and to mechanical engineering application. The new
developed plasticity model will be implemented in a finite element code and compared
with simple experimental results (monotonic and cyclic tests). This research is part of a cooperation with Prof. H. Sehitoglu (University of Illinois, Urbana-Champaign) toward modelling of high temperature cyclic properties of materials forenergy applications.

 

We are seeking for a
candidate for a position of research assistant (March-December 2011)
in this research field: the candidate will then be able to obtain a PhD
position onto the same topic (PhD scholarship will start in Jan. 2012). Candidates should have a background on material models, plasticity and finite elements.

Candidates can submit their Cv to Dr. Stefano Foletti (stefano.foletti@polimi.it). 

 

REFERENCES

 

[1] Chaboche, J.L., 2008. A review of some
plasticity and viscoplasticity constitutive theories.
Int. J. Plasticity 24, 1642–1693.

[2] Jiang, Y., Sehitoglu, H., 1996a. Modeling
of cyclic ratcheting plasticity. Part I: development of constitutive relations.
ASME J. Appl. Mech. 63, 720–725.

[3] Cailletaud, G., 1992. A
micromechanical approach to inelastic behavior of metals.
Int. J. Plasticity 8, 55–73.

[4] Abdeljaoued,
D., Ben Naceur, I., Saï, K., Cailletaud, G., 2008.
A new polycrystalline
plasticity model to improve ratcheting strain prediction, Mechanics Research
Communications
.

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