Viscoelastic Indentation of Silicate Glasses

The time‐dependent viscoelastic deformation and flow of various types of silicate glasses are examined by the use of a pyramidal Berkovich indenter. It is demonstrated that a pyramidal indenter is an efficient microprobe for viscoelastic studies of glass‐forming materials at temperatures near the glass transition point. Some important rheological functions of silicate glasses are determined as functions of time on the basis of a linear viscoelastic constitutive equation for pyramidal indentation. The test results are theoretically related to the dimension of flow units of these glasses, suggesting that a model of thermally fragmented silicate clusters is appropriate for consistently understanding the present rheological test results. However, the microstructural details (crystallite‐like or network‐like microstructures) of fragmented clusters are not inferred from the rheological information.