Time-stress correspondence in viscoelastic materials: an equation for the stress and temperature shift factor

Stress-time correspondence principle discovered experimentally by O'Shaughnessy already in 1948 [1] is considered. Using the Doolittle formula for the viscosity as a function of free volume [2], an equation for the generalized temperature—stress shift factor aT,σ is obtained. An equation for the stress-dependent shift factor aσ follows as a special case. The equation for the temperature shift factor aT already derived in 1985 [3] and successfully used since also follows from the aT,σ formula.