Mode I crack propagation in hydrogels is step wise

Cracking is one of the critical issues in the design of hydrogels. Numerical simulations on porous materials indicated that cracks may not propagate smoothly but in a step-wise fashion. The purpose of this work was to verify if this was the case and to characterize crack propagation. Performing single edge notch tests, in water and in air, we demonstrated that under tensile loading a crack indeed propagates in a step-wise fashion. Moreover, we found that the stiffness of the hydrogel is related linearly with the lengths of the steps and hyperbolically with the time that each step needs to propagate and break.