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PhD opportunity at ONERA Lille, France

Fabrice Pierron's picture

Virtual Fields Method for the dynamic behaviour
characterisation of metallic materials under purely inertial loads

Inelastic material parameter identification is usually performed
using simple or standardized specimens and unidirectional loadings in order to
stress the specimen with a uniformed field (uni-axial tension, torsion, etc.). However,
these tests, called statically determined, become much more complex to analyse
especially when localisations phenomena occur for large strains and
consequently this method can not be physically justified for inelastic
behaviour models. The literature shows others experimental procedures to
identify the whole set of model parameters with only one test that does not
make use of standardized specimens and hypotheses regarding the uniformity of
the stress field applied to the specimen.

Among then, the Virtual Fields Method (VFM) is a very
interesting candidate that makes it possible to handle full-field measurements
without costly updating computations and stringent the boundary condition
requirements. The VFM is based on the Principle of Virtual Works (PVW) that
expresses integral stress equilibrium within the solid. The identification is
performed by comparing the virtual work of internal and external forces. In
linear elasticity, this identification procedure is direct, but for non-linear
behaviour models, this comparison has to be performed through a cost function
which needs to be minimized. Though iterative, this procedure does not require
a direct FE computation at each evaluation of the cost function, which makes it
extremely computationally efficient.
It is proposed here to extend this method to high
velocity loading conditions in which inertial forces  significantly affect the deformation process of
the material under dynamic loads. A few recent feasibility studies on this have
been released but not for  highly
non-linear material behaviour. Key scientific issue comprise the implementation
of inertial forces within the VFM, test specimen design and quantitative
full-field strain and acceleration measurements using ultra-high speed video

Dr Bertrand
Langrand (ONERA Lille, France)

Eric Markiewicz  (University of Valenciennes, France)

Prof. Fabrice Pierron (University of Southampton, UK)

ONERA (The French
Aerospace Lab), Lille, France
Desired candidate profile
Master Degree in mechanical engineering or related discipline
Ability to perform both numerical and experimental work
Restricted to EU citizens

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