Micro-macro mechanics of damage and healing in rocks

Abstract

This paper presents the state of the art of the theory of damage and healing mechanics, with a particular emphasis on the strategies available to relate the micro-scale of crystals, cracks and pores to the scale of a Representative Elementary Volume (REV). We focus on mechanical degradation and recovery of stiffness and strength. Damage and healing models formulated in the author's group are used as examples to illustrate and compare the reviewed micro-macro approaches, which include fabric enrichment, micromechanical formulations and homogenization schemes.

We conclude that:

(i) The framework of hyperplasticity, which does not require any postulate on the existence or uniqueness of yield functions and which automatically ensures thermodynamic consistency, was never applied to Continuum Damage Mechanics (CDM). There may be an avenue to improve state-of-the-art damage and healing models in a similar framework of ``hyper-damage mechanics''.

(ii) Mesh dependency in softening models is currently alleviated by non-local regularization. However, healing can only happen where damage localizes. Perhaps the next step is to couple micro-macro damage and healing models at the REV scale to discrete fracture mechanics at a larger scale to understand how damage and healing localization occurs.

(iii) There may be an opportunity to use fabric-enriched models to capture the effect of microstructure organization on both mechanical properties and permeability.

(iv) Coupling chemo-mechanical damage and healing processes across the scales would be useful to model the competition between damage and healing whenever both can occur at the same temperature and pressure conditions.

(v) Many challenges still exist to implement healing models in the Finite Element Method, especially in regards to the mapping of net damage.