Derivation of Shift Factor for the Optical Glass Using Viscosity Measurement

In this study, the parallel plate test which is a kind of viscosity measurement technique was carried out to estimate the shift factor for optical glass. This method can reduce the measurement time in comparison to conventional creep test. First, deformation rates were calculated from histories of the displacement, which were then substituted in Gent’s equation for deriving the viscosities. The estimated viscosities indicated the temperature dependency in the viscoelastic range. Moreover, the shift factors obtained from parallel plate tests agreed well with those from static compression creep tests. Therefore, it was confirmed that the parallel plate test is an effective method for the derivation of shift factor for optical glass. In addition, the shift factors were almost same for measurement loads between 196 to 980 N.