Analyses on Time-dependent Fracture and Surface Instabilities of Polymeric Gels

Abstract

Polymeric gels which consist of a solid polymer network and liquid solvents swell when the solvents are absorbed into the polymer network and shrink when the solvents flow out of the polymer network Mechanical properties of polymeric gels including fracture properties are important for many applications The time-dependent fracture phenomenon of polymeric gels is affected by fluid diffusion which is strongly influenced by the initial pore pressure field attributed to loading and permeability conditions on the boundaries In this study the concurrent solid deformation and fluid migration for a center crack of finite length in a poroelastic medium subjected to uniaxial remote stress or strain is analyzed Four mixed types of permeability conditions on the remote boundaries and the crack faces are considered The instantaneous fracture energy is evaluated by a novel method which uses J-integral around the cohesive zone embedded ahead of the crack tip in the simulations The numerical results of are validated with the asymptotes predicted by stress intensities at small flow times When there is a difference between the imposed pore pressure and the initial pore pressure caused by applying loading on the boundaries the variation in is affected by short and long ranges of fluid flow and reaches its drained limit at a time on the order of where is the consolidation coefficient of porous materials The drained limit may not be the maximum value of especially when the difference on the remote boundaries is positive under strain control For stress-control cases whether the maximum occurs before drained state depends not only on the difference in pore pressure but also on where the permeable boundaries are When a solid network of a polymeric gel is found to exhibit viscoelastic behavior the fracture phenomena can be affected by both flow-induced and viscoelastic deformations This study analyzes the concurrent deformation of a mode-I center crack in a poroviscoelastic medium subjected to biaxial remote stresses for short-distance fluid flow For the drainage time differing from the viscoelastic relaxation time the curve exhibits a two-stage behavior When viscoelastic relaxation is completed before fluid drainage the value of at first changes from the unrelaxed-undrained limit to the relaxed-undrained limit and continues to increase till the relaxed-drained limit When viscoelastic relaxation is postponed until after fluid drainage the value of increases till the unrelaxed-drained limit and continues to increase till the relaxed-drained limit This study predicts the four aforementioned limits and shows excellent agreements with numerical results Polymeric gels may incur large deformations and increase the volume by several times after swelling Owing to the restrictions on lateral expansions and surface imperfections the instabilities may appear in the form of wrinkling Wrinkling is strongly governed by the compressibility of swollen gel confinements and gel thickness This study investigates surface wrinkling of a gel layer under arbitrary lateral confinements in the equilibrium state of swelling based on perturbation analysis This work also discusses possible gel-solvent systems of wrinkling under different confinements At equal biaxial confinements the wrinkle pattern is a combination of plane waves with the same wavelength in all directions Meanwhile at non-equal biaxial confinements the wrinkle pattern may be a sum of plane waves with dissimilar wavelengths and corresponding directions

Date of Award	2018 Jul 26
Original language	English
Supervisor	Yu-Yun Lin (Supervisor)