The applicability of a laser-speckle extensometer to the viscoelastic study of brittle materials at elevated temperatures is examined by the use of a soda-lime glass at various temperatures above the glass transition point for three different rates of tensile loading. The well-known thermorheological time-temperature superposition procedure in the observed stress vs. time curves successfully yields their master curve at the standard temperature. The shift factor aT used for superposition and

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... stress relaxation function E(t), both of which are determined in this stress vs. time master curve, agree quite well with the results in litera ture. The potential capability of using laser-speckle techniques for a large-scale elongation, such as a super plastic elongation, is also addressed.