3.3 Softening Point (SP)
The softening point is the temperature at which glass deforms under its own weight. Viscosity of the glass is 107.65 dPa·s {poise} at this temperature. The softening point is measured in accordance with the Fibre Elongation Method prescribed in JIS-R3104 and ASTM-C338.6.
3.4 Transformation Temperature (Tg) and Yield Point (At)
The transformation region is that temperature range in which a glass gradually transforms from its solid state into a "plastic" state. The transformation temperature (Tg) can be determined from the thermal expansion curve (Fig. 1). Viscosity coefficient at this temperature is approximately 1013 dPa·s {poise}.
Yield point (At) is the deformation point temperature on the thermal expansion curve, or the point at which elongation becomes zero.
| Fig. 1: Thermal Expansion Curve |