The Role of Surface Forces in Subcritical Crack Growth and Healing

Sponsor: Lawrence Berkeley National Laboratory

Duration: 10/1/2020- 12/14/2022

Role: Sole PI

Objectives

This is a collaborative research between CUBoulder and the Geoscience team at the Lawrence Berkeley National Laboratory, aiming to promote fundamental understanding of subcritical crack growth and healing in calcite.

Subcritical crack growth (SCG) is relevant to many geological processes at different length and time scales, e.g., time- and rate- dependent deformation of brittle rocks, relaxation of internal stresses in rock systems and delayed earth ruptures. The intricate coupling between physiochemical processes (i.e., adsorption and diffusion) and mechanics (i.e., stress concentration and crack opening) at the vicinity of the crack tip, however, has never been fully resolved. Significant pressure can develop when two solid surfaces are brought close to each other (which is the case at the crack tips), causing the solid-fluid interaction zones of the two surfaces overlap. This pressure, often referred to as the disjoining pressure, can be attractive and repulsive depending on the wall separation and the fluid chemistry. Its effect on the apparent fracture toughness (KI0) has been largely ignored in fracture mechanics and SCG literatures.

This study will test the hypotheses that the KI necessary to propagate cracks in aqueous environment (KI0) is reduced from the intrinsic value (KIC) because of the repulsive disjoining pressure developed between the fracture surfaces. Specifically, we plan to develop a surface-based fracture theory (SFFT) for modeling SCG, where the surface force and its variation with respect to environment serves as the central building block. The other key ingredients are the species transport equation in a varying aperture slit, and fracture mechanics solutions of crack opening profile and stress intensity factor. The ultimate goal of this project is to offer bottom-up predictions of environment-enhanced SCG in glasses and calcite.

Schematic of surface-force based fracture theory in modeling SCG.

Collaborators

Benjamin Gilbert, Ph.D., LBNL

Seiji Nagakawa, Ph.D., LBNL

Hang Deng, Ph.D., LBNL

Steven Pride, Ph.D., LBNL

Publications

Eskandari-Ghadi, M., Hang, D., Nakagawa, S., Pride, S., Gilbert, B., Zhang, Y. (2022) Surface force and reactant transport as the central mechanisms for subcritical crack growth: a theoretical study. In preparation.