Rupture of emerging tough hydrogels has received much attention in recent years. It is a fundamental question what length of initial flaws can significantly affect the rupture of a tough hydrogel. Here we study the rupture of a tough hydrogel, using samples with and without initial cuts, under monotonic and cyclic loads. We prepare six samples under the same conditions, either without initial cut, or with initial cuts of the same length, and load them monotonically to inspect the statistical variation of measured rupture stress, rupture stretch and work of rupture. We cycle the six samples in parallel to the same amplitude of stretch and record the number of cycles to rupture of each sample. The average number of cycles to rupture decreases with the amplitude of stretch; and an endurance stretch exists, below which the samples can sustain indefinite number of cycles without rupture. We find that when the initial cut is long, the endurance stretch decreases with the initial cut length. When the initial cut is short, the endurance stretch is insensitive to the initial cut length. We interpret this finding by a material-specific length, the endurance fractocohesive length. We compare the endurance fractocohesive lengths of the hydrogel and other materials, including elastomers, plastics, metals, and ceramics. It is hoped that similar experiments will be soon conducted for other hydrogels to guide their development.

近年来，新兴的坚韧水凝胶的破裂受到了很多关注。一个基本的问题是，初始缺陷的长度可以显着影响坚硬水凝胶的破裂。在这里，我们研究了在单调和循环载荷下有无初始切口的坚硬水凝胶的破裂。我们在相同的条件下准备了六个样品，这些样品既不具有初始切口，也具有相同长度的初始切口，并单调加载它们以检查测得的断裂应力，断裂拉伸和断裂功的统计变化。我们以相同的拉伸幅度平行循环六个样品，并记录每个样品破裂的循环次数。断裂的平均次数随着拉伸幅度的增加而降低。并存在耐力范围，低于此值，样品可以维持无限次的循环而不会破裂。我们发现，当初始切割较长时，耐力拉伸随初始切割长度而减小。当初始切割很短时，耐力拉伸对初始切割长度不敏感。我们通过特定于材料的长度（耐久分数内聚力长度）来解释这一发现。我们比较了水凝胶和其他材料（包括弹性体，塑料，金属和陶瓷）的耐久分数内聚长度。希望不久将对其他水凝胶进行类似的实验，以指导其发展。我们通过特定于材料的长度（耐久分数内聚力长度）来解释这一发现。我们比较了水凝胶和其他材料（包括弹性体，塑料，金属和陶瓷）的耐久分数内聚长度。希望不久将对其他水凝胶进行类似的实验，以指导其发展。我们通过特定于材料的长度（耐久分数内聚力长度）来解释这一发现。我们比较了水凝胶和其他材料（包括弹性体，塑料，金属和陶瓷）的耐久分数内聚长度。希望不久将对其他水凝胶进行类似的实验，以指导其发展。