Computational investigation of cavitation phenomena in physically assembled gels

Cavitation rheology is a novel technique to probe local mechanical properties of soft materials. In this experiment, a defect is introduced in the gel by inserting a needle connected to a syringe pump. The growth of defect subjected to a pressure load is recorded. At critical pressure, the defect becomes unstable and suddenly expands into a cavity leading to a drop in pressure. For physically assembled gels, experimental studies demonstrate critical pressure as high as ten times of that calculated analytically using hyperelastic models. We present a finite element modeling approach to capture the coupled effect of material modulus, viscous dissipation, surface tension, and geometry confinement in determining the critical pressure. Our results indicate that a portion of pressure applied to expand the defect dissipates through stress relaxation mechanism, thus, pumping rate influences the critical pressure. Surface tension restricts the expansion of defect while the confinement introduces an artificial stiffening response to the gel, hence, increase the critical pressure. We will also compare the finite element analysis results with that obtained from cavitation experiments.