A subcritical microcrack informed creep-damage model for quasi-brittle materials

A subcritical microcrack informed creep-damage model is proposed to describe the creep-failure behavior of quasi-brittle materials where the subcritical microcracks propagation is characterized by the subcritical damage. Total free energy is decomposed into the time-dependent component and time-independent component where the time-dependent Helmholtz free energy is associated with time-dependent behavior. Driven by the time-dependent free energy the subcritical damage growth is originated from the nano-scale fracture kinetics. Within the continuum damage framework, a modified stochastic damage model is introduced to account for instantaneous behavior and subcritical damage evolution. The viscoelastic behavior is characterized by the Burgers model. The proposed model is validated through several numerical simulations including uniaxial loading tests, uniaxial creep tests and bending creep test. The results demonstrate that the present model is promising for the long-term analysis of underground structures.