Ultrasoft Fracture Energies via Cavitation Rheology

The developing technique of cavitation rheology (CR) probes hydrostatic failure via void pressurization. Hydrostatic failure is hypothesized as a primary injury mechanism in blast and blunt force trauma and can be a side-effect of ultrasound therapies. More fundamentally, no standard method has been developed for the determination of failure properties in ultrasoft polymer networks. Past CR measurements of synthetic, polymeric materials at length scales from mm’s to μm’s have been found to correlate with elastic modulus and fracture energy. This technique is performed via pressurization of fluid within a needle that is embedded within a material. Crack shape is quantified using micro-computed tomography and shown to transition from being roughly penny-shaped, to lobed, to spherical as a function of microstructure (swelling and cross-linking). Our morphology map predicts crack shape as a function of microstructure. By combining scaling analysis with cavitation rheology boundary conditions, we generate quantitative fracture energies for ultrasoft polymer networks that are consistent with fracture energies obtained from the pure shear test geometry.