Possibility to Describe the Alternating and Nonmonotonic Time Dependence of Poisson’s Ratio during Creep Using a Nonlinear Maxwell-Type Viscoelastoplasticity Model

—A physically nonlinear constitutive equation with four arbitrary material functions for isotropic rheonomic materials is studied to determine the rheological effects simulated by it and the spheres of influence of the material functions. The properties of the volumetric, axial, and lateral creep curves generated by this equation and the dependence of the lateral strain coefficient (Poisson’s ratio) on the material functions, time, and stress during creep are analytically investigated. A general exact estimate of the upper and lower bounds of the Poisson’s ratio and criteria of its negativeness, increase, decrease, and constancy are obtained. The Poisson’s ratio of the model is proved not to be a nonmonotonic function of time.