As explained in some details in [2], the following aspects of the cell must be adequately taken
into account to capture the key features of its mechanical behaviour.
Lining and potshell interaction
The response of the cell is strain-driven. Thermal expansion and chemical swelling
generate elastic and potentially permanent deformation due to the confinement effect.
The stress state of the lining therefore depends on the combined response of the cell
components and the shell. The dilatometric and stress-strain behaviour of the cell
materials must accordingly be known accurately.
Lining mechanical behaviour
The nature of several dense refractory materials, for instance the prebaked carbon
cathode blocks, is very similar to that of concrete they exhibit a quasi-brittle response.
Some of their characteristics include the fact that their tensile strength is but a fraction of
their compressive strength, that they can still bear some load after cracking and that
their strength increases with confinement.
Material transformation and time-response
Preheating is intrinsically a transient problem. The response of the cell, for example the
opening of gaps at the block-to-paste interface, will depend on the timing of several time-
dependent phenomena. Ramming paste baking induces irreversible changes in its
microstructure, which leads to macroscopic effects like swelling and subsequent
contraction. The time-response of the paste to a sustained load (also known as creep)
also depends on its baking state: it is obviously much more plastic when green.
Cell construction
Most of the cell components are laid without a strong bond between them. As in a
masonry structure, joint behaviour has a profound effect on the stiffness and the
response of the system. Contact interfaces must therefore be modeled to identify
potential gap openings.
Also, for cell electrodes rodded using cast iron, the cast iron-to-carbon interface is
critical. As shown in [3], contact may not occur everywhere, the contact resistance is
pressure and temperature dependent, such that the thermal, electrical and mechanical
responses are coupled primarily through Joule heating and thermal expansion.