| Summary: | Recent short pulse (femtosecond) laser experiments have shown the existence
of a so called superelastic precursor for short time periods after shock wave
formation. The superelastic precursor is characterised as having amplitude far
greater than the Hugoniot Elastic limit.
This work reviews the current orthotropic thermoelastic plastic-damage model
developed at Cranfield University, which includes the ability to model high
velocity, shock wave forming impacts. The current model is unable to reproduce
the superelastic precursor. Recent methods of looking at plasticity are reviewed
and model improvements are suggested to enable the Cranfield model to
reproduce superelastic precursor waves. The methods investigated are both
dislocation based as it is determined that it is necessary to model deformation
on the microscale in order to achieve reproduction of phenomena on the
timescales of the early stages of shock wave formation and propagation. The
methods investigated are the so-called self-organisation of dislocations and a
mobile and immobile dislocation method proposed by Mayer.
The plasticity part of the model proposed by Mayer is suggested for further
investigation, including implementation into the DYNA 3D hydrocode which
contains the current Cranfield model, to numerically asses the models
capabilities. Similar, the self-organisation model is put forward for further
numerical analysis.
Further, calculation of the continuum Cauchy stress using purely atomistic
variables is investigated in the form of the virial stress. It is determined that the
virial stress calculation is unsuitable for modelling shock waves, however an
alternative atomistic stress calculation which is more suited to shock waves is
discussed. It is proposed that this stress calculation could be used to investigate
the stresses contained within the thin shock front.
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