Expanding Inertial Microcavitation Rheometry to Cover Large Material Stretches in Soft Materials

Abstract

The existence of cavitation in soft materials introduces challenging problems as it exhibits unique deformation and failure mechanisms. Soft materials behave differently under high strain-rates than under quasi-static loading conditions. Particularly, the effects of strain-rates in the ballistic and blast ranges are unknown. Laser-induced cavitation (LIC) is a thermally driven inertial process for generating large deformations at high to ultra-high strain-rates in optically transparent materials by way of cavitation. This study focuses on LIC as a reliable and robust experimental method for characterizing the constitutive response of materials across an order of magnitude in material stretches. Through the integration of an appropriate theoretical framework, material stresses and strains during cavitation can be estimated for homogeneous, isotropic materials with Inertial Microcavitation Rheometry (IMR), a tool developed to characterize the nonlinear viscoelastic properties of soft materials at high strain-rates. The long-time bubble radius at mechanical equilibrium and maximum bubble radius, defined as the material stretch in the hydrogel, determine the initial gas pressure in the bubble to initialize the simulation. However, the current theoretical framework was developed with limited experimental modulation of bubble amplitude, limiting the regime of accessible material deformations. Furthermore, the model neglects to address inelastic material behavior at large material stretches. In this work, an extensive library of material stretches due to bubble oscillation are experimentally achieved to identify critical material stretches during the transition from viscoelastic to inelastic behavior by systematically controlling bubble amplitude and material deformations over a large stretch range. This library of material stretches defined by the bubble dynamics are used in the simulation to test the robustness of IMR, and identify new avenues for future theoretical and numerical developments. In sum, this critical experimental data will lay the foundation for incorporating damage and failure mechanisms of inelastic behavior of soft materials undergoing high strain-rate deformations.