Experimental exploration of fluid-driven cracks in brittle hydrogels

Abstract

Hydraulic fracturing is a procedure by which a fracture is initiated and propagates due to pressure (hydraulic loading) applied by a fluid introduced inside the fracture. In this study, we focus on a crack driven by an incompressible Newtonian fluid, injected at a constant rate into an elastic matrix. The injected fluid creates a radial fracture that propagates along a plane. We investigate this type of fracture both theoretically and experimentally. Our experimental apparatus uses a brittle and transparent polyacrylamide hydrogel matrix. Using this medium, we examine the rate of radial crack growth, fracture aperture, shape of the crack tip and internal fluid flow field. Our range of experimental parameters allows us to exhibit two distinct fracturing regimes, and the transition between these, in which the rate of radial crack propagation is dominated by either viscous flow within the fracture or the material toughness. Measurements of the profiles near the crack tip provide additional evidence of the viscosity-dominated and toughness-dominated regimes, and allow us to observe the transition from the viscous to the toughness regime as the crack propagates. Particle image velocimetry measurements show that the flow in the crack is radial, as expected in the viscous regime and in the early stages of the toughness regime. However, at later times in the toughness regime, circulation cells are observed in the flow within the crack that destroy the radial symmetry of the flow field.

Symmetric coalescence of two hydraulic fractures

“…2 A-E. We can see from Fig. 2A that, initially, the flow was mostly radial, similar to that observed for single fractures (7). Then, after the fractures coalesced, the flow everywhere was attracted toward the bridge, and a large increase in velocity occurred in the vicinity of the bridge (Fig.…”

“…Newtonian fluids, water-glycerin mixtures with different dynamic viscosities µ, were injected at constant volumetric rates Q0 into the hydrogel using a syringe pump (HA PhD Ultra). The experimental parameters (Materials and Methods) were chosen so that the fractures propagated in the toughness-dominated regime before coalescence (7,9,11).…”

“…Recent experimental studies on single penny-shaped fractures successfully captured the dynamic behaviors for the propagation under two different dominant energy dissipation mechanisms: viscous dissipation and material toughness (7)(8)(9). In this paper, we focus on the coalescence of two fluid-driven, penny-shaped fractures when the fracture is dominated by the material toughness (rather than vicious dissipation) and provide experimental observations and scaling arguments on the dynamic behavior during the growth of bridges formed between two fractures.…”

Growth of gas-filled penny-shaped cracks in decompressed hydrogels

“…These assumptions are broadly consistent with the limited number of observations of small (t 1 mm) bubbles in hydrogels mimicking artificial tissues. 15,16 However, the forced syringe injection of liquid 17,18 or gas 19 into hydrogels is known to cause large (c 1 mm) cracks that are non-spherical and that grow by irreversible fracture of the material.…”

Tumescent Injections in Subcutaneous Pig Tissue Disperse Fluids Volumetrically and Maintain Elevated Local Concentrations of Additives for Several Hours, Suggesting a Treatment for Drug Resistant Wounds

“…We know of no synthetic material of similar density that can dilate by such a large factor without cracking. The same experiment in gelatin, for instance, creates a crack whose leading edge propagates as more fluid is injected [25,26].…”