Effect of crosslinking on the mechanical properties of multiple network elastomers: experiments and modeling

Multiple network elastomers (MNEs) consist of a highly crosslinked sacrificial network and one or more loosely crosslinked matrix networks. Their outstanding mechanical properties are highly sensitive to the design of crosslinker density. This study explores how the crosslinking degree of the sacrificial network affects the mechanical behavior of double/triple network elastomers (DNE/TNE) through a combination of experiments and modeling. Cyclic loading tests show negligible hysteresis in DNEs, regardless of the crosslinking degree. In contrast, TNE exhibits prominent hysteresis that increases with crosslinker density. A progressively damaged model is further developed to describe the stress response. The results show that as the crosslinking degree increases, the peak of the probability density-chain length distribution curve becomes higher and shifts leftward, indicating a decrease in average chain length. The fracture tests reveal that the fracture toughness of MNEs first increases and then decreases with increasing crosslinker density. Notably, in TNE, although energy dissipation continues to rise with crosslinking degree, fracture toughness does not increase accordingly, suggesting that the fracture toughness of MNEs is not solely dominated by energy dissipation. These findings offer valuable insights for tailoring the modulus, energy dissipation, and fracture toughness of MNEs.