A model of the fracture of double network gels

I propose a very simple model accounting for the very high toughness of double network gels based on the assumption that the first, stiff network will break up forming multiple cracks when the stress is above a defined value. These cracks are held together by the second network. A multiply cracked damage zone will form around any macroscopic crack in the material, causing energy dissipation and shielding the second network. The toughness enhancement by this process is estimated to be about x40. The effect of cross-linking of the second network is discussed and explained.