Yida Zhang

We develop a large-strain poromechanics theory for the coupled sorption–deformation behaviours exhibited by many soft nanoporous materials. Instead of modelling sorption as a molecular mixing process as in classical gel theories, we interpret it as a nanopore-level phenomenon that alters pore-scale interactions and thereby affects the macroscopic response of the porous solid. The proposed theory primarily follows the poromechanics formulation of Coussy (Coussy 2004 Poromechanics. Chichester: John Wiley & Sons, Ltd) and its enrichment with surface thermodynamics (Zhang 2018 J. Mech. Phys. Solids114, 31–54). Specifically, we treat the system as a three-phase mixture by separately listing the balance laws of the solid, the bulk fluid and the sorbed excess phases, which are then combined to deduce the free energy imbalance of the system. Examining individual dissipation terms leads to the general forms of transport laws, reaction kinetics, constitutive relations of the porous solid and the equations of state (EOS) of the bulk and the excess fluids. We demonstrate that, in the presence of sorption, the equivalent pore pressure that drives changes of fluid-accessible porosity is no longer solely the bulk fluid pressure, as assumed in traditional poromechanics theories, but includes an additional disjoining pressure arising from the sorbed excess. We confirm that the disjoining pressure isotherm and the sorption isotherm are fundamentally the two sides of the same coin, both characterized by the free energy potential of the excess phase. A simple four-parameter model for amorphous cellulose (AC) interacting with water vapour is constructed using only elementary, textbook-level constitutive laws for the individual phases. Despite its simplicity, the model exhibits remarkable predictive capability in capturing the complex, nonlinear sorption–deformation coupling of the material. Finally, we show that the chemomechanical formulation of Gurtin et al. (Gurtin et al. 2010 The mechanics and thermodynamics of continua. Cambridge University Press) and the gel theory of Hong et al. (Hong et al. 2008 J. Mech. Phys. Solids56, 1779–1793) can be retrieved by reducing the ‘resolution’ of the proposed theory through eliminating the porosity terms and combining the bulk fluid and the sorbed excess phases. The modularity and versatility of the proposed theory make it well-suited for applications beyond polymeric materials, extending to a broad class of nanoporous systems with diverse microstructures and physicochemical interactions with surrounding fluids.

Wildfires can play an important role in shaping bedrock‐dominated landscapes. Fire can break down rock by spalling exposed surfaces. In massive rock, spalled flakes tend to be of the order of 1 cm thick and several to tens of centimeters in diameter. In central Australia, erosion rates from fire‐induced rock spalling have been proposed by Buckman et al. (2021, https://doi.org/10.1038/s41467‐021‐22451‐2 ) to result in unique overhangs called flared slopes that ornament the base of bedrock outcroppings (inselbergs) that dot the otherwise flat landscape. The long‐term evolution of rock surfaces exposed to repeated fires inspires our numerical modeling of the fire spall process. We honor the radiative balance on the rock wall and address two fire geometries. We incorporate a thermally modulated damage criterion to mimic the cracking of the rock. The penetration depth of the thermal perturbation is scaled by the square root of the duration of the fire, reaching many cm for a tree fire, and several mm for a brush fire. Modeled erosion of rock walls due to repeated fires is rapid at first but slows as the distance to the fires increases. The emergent steady shape is scaled by the height of the vegetation. The pattern of radiation from a tree fire, and the predicted damage caused by it, mimic the geometry of flared slopes that ring Australian inselbergs, supporting the hypothesis of long‐term wildfire driven lateral erosion of these features. The timescale predicted is an order of magnitude larger than the erosion rates measured across the inselberg tops in previous work.

Subcritical crack growth (SCG) plays an important role in many geological processes such as delayed earth rupture and rock weathering. The complex dependency of SCG on the in‐crack fluid chemistry, however, is still poorly understood. In this study, we utilize the newly developed surface force‐based fracture theory (SFFT) to elucidate the relative contributions of surface forces and solute transport to the crack growth kinetics of calcite in NaCl solutions. Expanding on Barenblatt's cohesive crack model, SFFT introduces an effective stress intensity at the crack tip that encompasses all the relevant intermolecular forces across the crack in addition to the external far‐field stresses. The nonlinear system of equations portraying the crack opening profile, the solute distribution in a propagating crack, and the crack growth velocity are numerically solved via an implicit scheme. After carefully calibrating the model for calcite‐water systems, the SFFT is used to predict the SCG response of calcite at different NaCl concentrations, based on various hypotheses. These predictions are then compared to existing SCG data from the literature. We demonstrate that the experimentally observed variation of SCG rate with NaCl concentration cannot be explained solely by DLVO forces (electrostatic and Van der Waals interactions). This can be remediated by introducing an exponentially decaying hydration force with a nonlinear, nonmonotonic dependence on NaCl concentration. Furthermore, we demonstrate that accounting for both diffusive and advective transport of ions is important in explaining the absence of a stage‐II SCG response for calcite in electrolyte solutions.

Fabric-based jamming phase diagram, where F _t and Z _t are the fabric anisotropy (deviatoric invariant of the 2nd order fabric tensor) and the coordination number (mean invariant of the 2nd order fabric tensor) of the total-contact network, respectively.

The susceptibility of a granular soil to suffusion is strongly dependent on its grain size distribution (GSD) and the mechanical and hydraulic conditions it is subjected to. This study investigates the onset of suffusion considering the effect of confining pressure and stress anisotropy using a fully resolved computational fluid dynamics and discrete element method (CFD–DEM). Three benchmarks, including the sedimentations of single and two adjacent spheres and the classic one‐dimensional (1D) consolidation are performed to demonstrate the capability of this method for high‐fidelity particle‐fluid simulations. A modified hydraulic criterion for the onset of suffusion considering stress anisotropy is presented. The microstructural changes of soil specimens before and during global suffusion are inspected, with emphasis on the evolutions of particle kinetic energy and displacements, force chain networks, and stress anisotropy. We found that the critical hydraulic gradient is negatively correlated with the confining pressure and the degree of stress anisotropy. Fine particles in the soil matrix are locally detached at small hydraulic gradients before the apparent global suffusion, as manifested by the variation of particle kinetic energy and coordination numbers. The roles of different contact types on force transmission and stress anisotropy in eroded specimens are also examined.