Meaning
Industrial glass and polymer processors use a multi-parameter mathematical model to simulate how the glass transition temperature and structural state evolve during varying thermal cycles. The tool-narayanaswamy-moynihan model defines this evolution, using a non-linear calculation that accounts for both the temperature dependence and structural state of the material. It establishes the limits of simple thermal calculations by introducing the concept of fictive temperature to represent the non-equilibrium state of the glass.
This model is a standard tool for predicting stress and volume changes during cooling.
Fictive Temperature
The structural state of a glass is characterized by a temperature that corresponds to the structure frozen in equilibrium. In the tool-narayanaswamy-moynihan model, the fictive temperature lags behind the actual temperature during cooling and relaxations. If the cooling rate is fast, the fictive temperature is high, which indicates a less dense and less stable structure.
This calculation allows engineers to design heat-treatment cycles that minimize residual stress.
Parameter Calibration
Calibrating this model requires differential scanning calorimetry tests that track the heat capacity across the glass transition region. These tests provide the parameters for activation energy and non-linearity. It ensures accurate predictions.
Process Control
Applying this model to manufacturing ensures that plastic or glass components have uniform properties and low residual stress. It is used to design cooling schedules in optical lens fabrication. This optimization prevents optical distortion.
