Damage mechanism insights into double network hydrogels: Predicting cyclic loading behaviors via monotonic loading

During the internal fracture process of the double network hydrogels (DN gels), the coupling effect between the two networks impacts excellent tensile properties and energy dissipation capabilities to the DN gels. To better understand this coupling effect and uncover the underlying damage mechanism of DN gels, it is important to study their loading behaviors. In this study, we investigate the effects of the network composition on the deformation modes under monotonic loading and fracture toughness of the DN gels. The deformation modes are categorized into five types. Among these, we find that the “Ductile & Necking” DN gels exhibit both high fracture toughness and high fracture strain. We then propose a damage model to predict the cyclic loading behaviors of the “Ductile & Necking” DN gels based on monotonic loading. The damage model quantitatively captures the stress-strain relationship and the dissipated energy density of DN gels during cyclic loading. Furthermore, the proposed damage model is validated and extended to DN gels with various physical and chemical network structures, showing good agreements with experimental results. This study establishes a connection between monotonic loading and cyclic loading behaviors in DN gels through the proposed damage model, providing deeper insights into their damage mechanisms. Additionally, it offers valuable guidance for the synthesis and design of soft materials.