An internal state variable viscoelastic-viscoplastic constitutive equation with damage

Based on Rice internal state variable thermodynamics, the creep damage is discussed in constrained configuration space. An internal state variable viscoelastic-viscoplastic constitutive equation with damage under constant stress and temperature conditions is derived by giving specific complementary energy density function and evolution functions of internal state variables. Parameters identification and model validation are conducted under one dimensional scene through uniaxial creep test of analogue material by load and unload method. The proposed constitutive equation can describe viscoelastic strain and three phases of creep preferably. Different stages accompany with different energy dissipation processes. The material system without damage tends to thermodynamic equilibrium state or steady state after disturbing by stress. During creep damage process, the material system has a tendency that is from closing to equilibrium state or steady state to departing from equilibrium state. The energy dissipation rate can be a measure of distance between current state and equilibrium state of material system; the time derivative of energy dissipation rate can characterize development trend of system, and their integral value in domain can be regarded as indexes to evaluate the long-term stability of structure.