Meaning
A mathematical expression models the temperature dependence of relaxation times for amorphous polymers near the glass transition temperature. The williams-landel-ferry equation calculates the shift factor for superposing data obtained at different temperatures into a master curve. This relationship remains valid within the range starting just above the glass transition temperature up to roughly one hundred degrees Celsius higher.
It relies on the free volume theory to describe how chain mobility increases with thermal energy.
Viscoelastic Shift
Moulders apply this principle when shifting time-temperature data to predict long-term creep or stress relaxation from short-term experiments. Correct analysis prevents part failure when the williams-landel-ferry equation guides the extrapolation of dynamic mechanical data for structural plastics. If the shift factor calculation fails, the predicted modulus values deviate from the physical reality of the resin inside the tooling environment.
Production Variance
Polymeric materials exhibit distinct behaviours when moving between virgin pellets and regrind mixtures due to changes in molecular weight distribution. A technician monitors these variations because the williams-landel-ferry equation defines the sensitivity of melt flow to thermal fluctuations during injection. Accurate control over the barrel temperature profile ensures that the viscosity remains stable throughout the cycle.
Failure to account for these dynamics increases the risk of short shots or flash in high-precision components.
Process Limit
Extrusion settings depend on this model to maintain consistent dimensions in films and profiles subjected to varying thermal histories. The williams-landel-ferry equation defines the operational envelope where the time-dependent mechanical response of the polymer remains predictable. Beyond this temperature region, other models provide more accurate descriptions of polymer behaviour.
The applicability of this model provides a reliable boundary for engineering design in thermoplastic applications.
