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Creep and glass transition

Creep is time-dependent deformation under constant load at high temperature, important for example in turbines and boilers. The glass transition temperature TgT_g of a polymer is the temperature where an amorphous polymer goes from hard and glass-like (and brittle) below TgT_g, to soft and rubbery above it.

creep: time-dependent deformation at constant load, high T\text{creep: time-dependent deformation at constant load, high } T
T<Tg:glassy, brittleT>Tg:rubbery, softT < T_g: \text{glassy, brittle} \quad T > T_g: \text{rubbery, soft}the polymer's state around TgT_g

Symbols

TgT_gglass transition temperature°C

Example

A rubber gasket that becomes stiff and cracks in severe cold has likely dropped below its TgT_g.

Creep only becomes significant at a high homologous temperature (near the melting point), not at room temperature for most metals.
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Part of Materials Technology: Heat treatment and corrosion.