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Gilles Dusserre
Abstract
Thermomechanical loading in a cast martensitic stainless steel mould while a glass pressing cycle
Gilles Dusserre - 14 December 2006
Glass pressing process is a forming process in which a glass gob
is squeezed between two tools. The use of cast stainless steel
moulds instead of wrought steel allows a decrease of the tooling
costs, but the life time of the hollow mould is consequently
decreased. The damages usually take place at the triple junction
of dendrites.
This thesis is a contribution to the improvement of these tools
life time. The aim is to determine the thermomechanical loads of
the mould during a glass pressing cycle. Two types of loading
exist: the thermal stresses caused by the gradient of thermal
dilatation caused by the heat transfer at the glass and mould
interface and the superficial stresses caused by the flow of the
glass along the surface of the die.
An instrumentation of an industrial mould has been realized in
order to measure the temperatures in the industrial context and
inform about the process (time cycle, use temperature...). An
inverse method has been used to estimate the heat flux density
at the surface of the tool during the cycle.
A high strain viscoelastic law is proposed and identified from
compression tests with cylindrical glass samples. The industrial
forming process is then simulated using this new rheological law
in order to determine the normal stresses on the mould while
pressing.
A cyclic plastic law is identified in order to take into account
the cyclic softening that characterizes martensitic steels
submitted to a cyclic mechanical loading.
The models, measurements and results of the above described
simulation are finally used to calculate the evolution of the
stress field in the mould during the pressing cycle, taking into
account the real condition of use of the mould as well as
possible. This data corresponds to the reference case of a
numerical parametric study whose aim is to quantify the
influence of some process or materials parameters on the
thermomechanical stresses in the mould.
Keywords :
Glass pressing process, Heat flux density, Viscoelasticity,
Tempered martensitic steels, Cyclic softening, Thermomechanical
stresses
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