INVESTIGADORES
IDIART Martin Ignacio
congresos y reuniones científicas
Título:
Bounding the plastic strength of polycrystalline solids with pressurized cavities
Autor/es:
M. I. IDIART; J. E. RAMOS NERVI
Lugar:
Mendoza
Reunión:
Congreso; XX Congreso sobre Métodos Numéricos y sus Aplicaciones; 2013
Institución organizadora:
Asociación Argentina de Mecánica Computacional
Resumen:
Nuclear fuel pellets in CANDU reactors are made
of polycrystalline natural uranium dioxide with a face-centered cubic symmetry.
As a result of their fabrication process and burn up during operation,
microcavities nucleate within the material at both intergranular and
intragranular levels. These cavities act as sinks for the fussion gasses
produced by neutron radiation. During incidental conditions, the gas pressure
within the cavities can rise significantly and cause swelling of the pellet by
plastic deformation. This can induce severe damage to the surrounding cladding,
allowing fission gasses to diffuse to the coolant. The mechanical loads
exherted by the pellet on the cladding depend on the thermomechanical behavior
of the polycrystalline pellet.
The elastoplastic deformation of a polycrystalline
material is to a great extent dictated by the morphology, lattice orientation,
and elastoplastic response of each individual single-crystal grain composing
the aggregate, the porosity, and the internal gas pressure. Relating the
macroscopic response with the microscopic properties is necessary to estimate
the deformation-induced plastic anisotropy that develops in these materials
when subjected to large deformations. Very often the response of these
materials is idealized as elastically rigid and plastically non-hardening.
Within this so-called rigid-perfectly plastic model, the above problem reduces
to finding the macroscopic yield surface of the polycrystal given the yield
surface at the single-crystal level and the statistics of the morphology and
orientation distributions of the grains and cavities. Due to their inherent
microstructural randomness, cognate polycrystalline solids do not exhibit a
single response but a ---hopefully narrow--- range of responses. In this work we
derive bounds for the range of possible responses.
To that end, we make use of the of a
comparison-medium method proposed by Idiart & Ponte Castañeda (Proc. R.
Soc. Lond. A vol. 463, 2007). The effect of internal pressure is then
introduced in the bounds via a suitable change of variables following the work
of Vincent et al. (Int. J. Solids Struct. Vol. 46, 2009). The method is applied
to various material systems in order to explore the simultaneous effect of
crystallographic symmetry and internal pressure level on the overall plastic
strength of polycrystalline solids.