Needle-induced-fracking in soft solids with crack blunting

Fracking, also known as hydraulic fracture, has been intensively studied in hard and brittle materials such as shale rocks and ice. In contrast, little is known about fracking in soft solids, especially with significant crack blunting. Recently, it has been found that during the needle-induced-cavitation experiments on soft gels or elastomers, the materials can be ruptured by pressurized fluid. Due to the large elastofracture length, a short crack in a soft solid during the fracking often shows severely blunted tips, and therefore, the crack extension and large deformation in the material become nearly indistinguishable in the experiments. In this letter, we propose to adopt a simple model, considering both large deformation and crack blunting, to predict the change of the hydraulic pressure during the needle-induced-fracking in soft solids. We found that the theoretical predictions agree very well with experimental data reported in the literature. The studies presented in this letter may provide new insights into the understanding of the fracking in soft tissues and cells, and lead to a facile way to measure fracture energy of soft materials, which can be very challenging for conventional testing methods.