Damage Poro-Mechanics group at GeorgiaTech (DeeP MeLT)
Poromechanics of Damage and Healing: A Philosophy of the Mesoscale
Damage is an abstract concept, generally associated to the ideas of degradation, decrease of performance or loss of reliability. Because damage is tied to the notion of deprivation, its definition is relative to a reference state and its measure depends on standards considered as relevant observation tools by the modeler. Damage prediction relies on the field variables chosen to describe the anticipated “degradation”, “loss” or “deprivation”. That is the reason why framing a damage model is necessarily a dynamic thinking process, well described by Claude Bernards’ OHERIC approach: Observation-Hypothesis-Experimentation-Interpretation-Conclusion. Healing can be understood as the microscopic processes underlying observable compensation (or recovery) of damage. However, while there is no consensus on the definition of healing in geomaterials, proven crack “sintering” and “re-bonding” do not stem from the same physical processes as the ones originating damage. The fundamental question is: “What do we want to observe?” In other words: “What is the mesoscale”?
We formulate energy-based damage and healing models for geomaterials – mainly rock and cement-based materials. The underlying theoretical background comprises fundamental thermodynamics, poromechanics, Continuum Damage Mechanics, micro-mechanics and homogenization schemes. Starting from observations reported by experimentalists, we postulate the form of thermodynamic potentials, and we define macroscopic variables that can be coupled to microscopic variables describing fabric evolution with crack opening, closure and healing. Most of our work focuses on damage – induced anisotropy of stiffness and permeability.
The keys for damage and healing phenomenological modeling are (1) the
choice of descriptors, i.e. the choice of a set of independent and complete variables
relevant to the macroscopic properties under study, (2) the scales of the
observation window, i.e. the length scales at which a continuum rheology may
and need to be defined. Emphasis is put on how descriptors evolve across the
· An alternative damage model was formulated in
independent strain variables, allowing to account for thermo-hydro-mechanical
couplings in unsaturated brittle rock,
An exploratory damage and healing model was
proposed, based on the evolution of an intermediate internal variable - defined
as the difference between a rate-independent damage variable and a
rate-dependent healing variable,
A novel permeability model was formulated to
update microscopic Pore Size Distribution (PSD) parameters with macroscopic
deformation and damage,
A thermodynamic framework was proposed to model
crack opening, closure and healing for one single crack embedded in a solid
The proposed approach allows predicting crack patterns around geological storage facilities and ahead of fracture tips, which is a central issue in energy geotechnics. Models are also expected to contribute to the design of self-healing geomaterials for sustainable infrastructure. The philosophical question is: does a (fixed) mesoscale exist, and is it unique?
Pereira, C. Arson, 2012. Retention and Permeability Properties of Damaged
Porous Rocks, Computers & Geotechnics, DOI: 10.1016/j.compgeo.2012.08.003
2. C. Arson, J.-M. Pereira, 2012.
Influence of Damage on Pore Size Distribution and Permeability of Rocks,
International Journal for Numerical and Analytical Methods in Geomechanics, DOI:10.1002/nag.1123
3. C. Arson, H. Xu, F.M. Chester, 2012.
On The Definition Of Damage In Time-Dependent Healing Models For Salt Rock,
Géotechnique Letters, vol.2, pp.67-71
4. C. Arson, B. Gatmiri, 2010. Numerical
study of a thermo-hydro-mechanical damage model for unsaturated porous media,
Annals of Solid and Structural Mechanics, vol.1, n.2, pp. 59-78
5. C. Arson, B. Gatmiri, 2008. On damage
modelling in unsaturated clay rocks, Physics and Chemistry of the Earth,
vol.33, pp. S407–S415