Delayed fracture in gels
Delayed fracture in gels
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DOI：
10.1039/c2sm25553g
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发表时间：
2012-07
期刊：
影响因子：
3.4
通讯作者：
Xiao Wang;Wei Hong
中科院分区：
文献类型：
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作者：
Xiao Wang;Wei Hong
在亚临界载荷作用下，溶胀的聚合物凝胶可能会犹豫很长一段时间而不表现出任何宏观症状，然后突然破裂。这种现象通常称为凝胶的延迟断裂。在本文中，我们从连续介质和断裂力学的角度提出了凝胶延迟断裂的可能机制。使用聚合物凝胶的连续粘孔弹性模型，我们计算了由于粘弹性蠕变和溶剂迁移耦合而导致的预先存在的裂纹周围的不均匀应力场的演变。我们将瞬时能量释放率作为裂纹的局部驱动力，并发现它是时间的递增函数。排除粘弹性蠕变和溶剂迁移的耗散，裂纹扩展的标准是瞬时能量释放速率等于聚合物的固有断裂能。因此，断裂延迟可归因于粘弹性蠕变和溶剂迁移使瞬时能量释放速率达到固有断裂能水平所需的时间。对于大多数溶胀凝胶来说，溶剂迁移是限制过程，因此延迟时间取决于预先存在的裂纹的大小，与常见的扩散限制过程类似。最后，通过假设微裂纹的特定尺寸分布，我们为溶胀凝胶的寿命预测提供了简单的统计分析。
Subject to a subcritical load, a swollen polymeric gel may hesitate for a prolonged period of time without showing any macroscopic symptom, and then break suddenly. Such a phenomenon is usually referred to as the delayed fracture in gels. In this paper, we present a possible mechanism for the delayed fracture in gels from the continuum and fracture mechanics point of view. Using a continuum visco-poroelastic model for polymeric gels, we calculate the evolution of the inhomogeneous stress field around a pre-existing crack, in consequence of the coupled viscoelastic creep and solvent migration. We invoke the instantaneous energy release rate as the local driving force for a crack, and find it to be an increasing function of time. With the dissipation from viscoelastic creep and solvent migration excluded, the criterion for crack advancing is that the instantaneous energy release rate equals the intrinsic fracture energy of the polymer. The fracture delay could thus be attributed to the time needed for viscoelastic creep and solvent migration to bring the instantaneous energy release rate to the level of the intrinsic fracture energy. For most swollen gels, solvent migration is the limiting process, and therefore the delay time depends on the size of a pre-existing crack in a similar way as common diffusion-limited processes. Finally, by assuming a specific size distribution of microcracks, we provide a simple statistical analysis towards the lifetime prediction of a swollen gel.