High-Resolution Quasistatic Near-Crack-Tip Deformation Fields in Brittle Hydrogels


At the tip of a propagating crack, the stress field becomes singular - and diverges to infinity. In reality, this divergent stress is regularized, as material failure occurs; furthermore, the nature of the singularity at the crack tip can be fundamentally altered by material nonlinearities before the onset of failure. Despite the importance of the crack tip in governing the failure of materials, experimental data that fully resolve the deformation near the crack tip are lacking, and experimental progress is hindered by the large deformation in soft materials such as hydrogels. Here, we propose a high-resolution method that resolves the near-tip deformation field based on direct measurement of the deformation gradient tensor via a particle tracking algorithm. The particle tracking approach addresses shortcomings of large deformation/rotation scenarios near a free surface in existing deformation measurement methods. Using this method, we directly measured the displacement fields in the immediate vicinity of a quasistatic crack in a stretched polyacrylamide hydrogel. We furthermore quantify the error in our measurement of the components of the deformation gradient tensor, as developed from the particle displacement measurements. Using the deformation data, we determine the stress state with a neo-Hookean material model. These stresses are directly compared with classical LEFM theory and non-linear material model extensions to LEFM. Perspectives on employment of the method in 3D are provided.

Jul 5, 2022 12:40 PM — 2:40 PM
Galway, Ireland