Effect of the Initial Stage of Strain on the Properties of Relaxation Curves Generated by the Rabotnov Nonlinear Relation for Viscoelastic Materials

An equation describing a family of stress relaxation curves with arbitrary strain programs at the initial stage generated by the Rabotnov nonlinear constitutive relation with two arbitrary material functions is derived and studied analytically. The effect of the initial stage duration and shape on the properties of relaxation curves is analyzed. Their deviations from each other and from the relaxation curves under instantaneous load are estimated in terms of material functions and strain programs. The convergence of deviations to zero is proved when the time tends to infinity or when the initial stage duration tends to zero.