Stress Relaxation Modulus of a Commercial Glass

The stress relaxation modulus in compression of a container glass was investigated over a wide range of strain, time, modulus, and temperature. The glass is a linear viscoelastic liquid up to 2% strain, and the modulus is a smooth function of time, with no pseudorubbery plateau apparent down to a modulus of 10° dynes/cm². The data cover 4 decades in time and a range of almost 100°C above the glass transition, T ₀ =536°C. Within experimental error, changes in temperature simply shift the modulus-vs-time curve along the time axis without altering its shape. This behavior implies that the same mechanism controls both the bulk and shear spectra. The shift factors fit the WLF equation well with values for the parameters c₁ and c₂ of 16.7±0.2 and 345±5°C, respectively. Data from the literature for silicate glasses agree with these parameters.