Multi-crack formation in soft solids during high rate cavity expansion

The parameters governing failure in ultra soft solids can be difficult to quantify since traditional characterization techniques often cannot be implemented. The effects of increasing rate further complicate efforts. However soft solids, especially biological tissues, are frequently subjected to high rate deformation leading to damage and failure and should therefore be understood. We present results from high rate, needle-mediated cavity expansions in soft silicone and ballistic gelatin samples with moduli on the order of 10 kPa. We find that increasing rate of expansion increases the number of cracks initiated in the cavity surface, leading to multi-lobed as opposed to penny-shaped cracked cavities. Comparison of these experimental observations with an elastic wave speed-dependent fracture correlation model originally developed for hard materials suggests that counting the number of cracks may provide a measure of the soft solid's fracture energy.