Application of the network alteration theory for modeling the time-dependent constitutive behaviour of rubbers. Part I. General theory

The long-term time dependent irreversible deformation behaviour of rubber-like materials is characterized by large (irreversible) deformation, stress-relaxation, creep, permanent set and aging induced flexibility changes. These types of material behaviour are being described by combining the general (rubber) hyperelastic theory and Tobolsky's (network) alteration theory. To generalize Tobolsky's idea, the long-term time-dependent irreversible deformation behaviour is postulated as being caused by alterations of the original microstructure into new microstructures. This concept yields a general time-dependent constitutive model for rubberlike materials. Besides, the short-term rubber hysteresis behaviour (Mullins' effect) is adopted into the present model by implying the rubber hysteresis model of Simo. The experimental characterization of the model parameters - using the eight non-Gaussian chain theory for rubber elasticity as point of departure - as well as the experimental model verification are performed using modified Natural Indonesian Rubber samples. The experimental evidences will be presented in Part II (Septanika, E.G., Ernst, L.J., 1998. Application of the network alteration theory for modeling the time-dependent constitutive behaviour of rubbers. Part II. Further evaluation of the general theory and experimental verification. Mech. Mater. 30, 265-273). The present paper is concerned with the model development. (C) 1998 Elsevier Science Ltd. All rights reserved.