Abstract：Water diffusion in hydrogels significantly affects their mechanical behavior. Previous experimental studies on hydrogel fracture under water diffusion mainly focused on macroscopic crack observations, while experimental characterization of crack tip deformation fields in aqueous environments remained unexplored. Furthermore, theoretical analyses of water diffusion effects on crack tip deformation lack validation across different loading conditions. In this study, based on the digital image correlation (DIC) method, a self-designed mechano-chemical coupled tensile platform was employed to investigate the effects of water diffusion on crack tip deformation in polyacrylamide (PAAm) hydrogels under constant force and displacement loading. Experimental results reveal non-equilibrium diffusion competition mechanism at crack tip under different loading conditions. Finite element simulation based on a coupled large-deformation-diffusion theory was conducted to analyze the swelling ratio near crack tips under constant force loading. The simulation results confirm that stress-induced chemical potential gradients drive water accumulation at crack tips. Further, comparative experiments in oil and aqueous environments demonstrate that water exchange between hydrogels and their surroundings dominated crack tip deformation evolution.
2025, Vol. 46 
