Indentation rheometry for glass-forming materials

Theoretical considerations are made on the time-dependent viscoelastic deformation and flow during penetration by a flat-ended, spherical. conical, or a pyramidal indenter into glass-forming materials at temperatures near the glass-transition. The concept of representative stress and strain, combined with the hereditary integral leads to principal constitutive equations for linear viscoelastic indentation. An experimental study of the viscoelastic behavior of soda-lime Silica glass, as a representative of glass-forming materials, is conducted with the use of a trigonal sapphire indenter (Berkovich indenter). The self-consistency of the present theoretical framework for viscoelastic indentation is demonstrated on the basis of experimental results. It is emphasized that the indentation technique provides the most efficient micro/nano-probes for examining viscoelastic behaviors of glass-forming materials at temperatures near the glass-transition; testing specimens with extremely small dimensions and thin films with no special preparation, as well as testing with compressive loading for elevated temperatures. (C) 2001 Elsevier Science B.V. All rights reserved.