Fatigue of hydrogels
Fatigue of hydrogels
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DOI：
10.1016/j.euromechsol.2018.12.001
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发表时间：
2019-03-01
影响因子：
4.1
通讯作者：
Suo, Zhigang
中科院分区：
文献类型：
--
作者：
Bai, Ruobing;Yang, Jiawei;Suo, Zhigang
自20世纪60年代以来，水凝胶已被开发用于个人护理，医学和工程领域。已经积累的证据表明，水凝胶在长时间的负荷下会产生疲劳。症状包括性质的变化，以及裂纹的成核和生长。本文是对水凝胶疲劳研究的首次综述。重点放在化学疲劳的概念和实验，链接疲劳症状的分子过程。疲劳症状的特点是测试样品与不预切裂纹，受到长期的静态和循环载荷。我们描述了使用的能量释放率与预切裂纹的样品，在大规模的非弹性的条件下，复杂的流变学的水凝胶。突出显示的是三个实验设置：纯剪切，撕裂，剥离，能量释放率是很容易获得的任意流变材料。我们描述化学键和网络拓扑结构。非共价键和某些共价键是可逆的：它们在相关条件下断裂后改革。大多数共价键是不可逆的。网络的每一种拓扑结构都是连接可逆键和不可逆键的一种方式。我们回顾了五个代表性的网络拓扑结构的水凝胶的实验数据。我们比较了Lake-Thomas阈值、循环疲劳阈值和静态疲劳阈值。疲劳是一种分子疾病。疲劳的所有症状都源于一个根本原因：水凝胶的分子单元在长时间的负荷下改变邻居。疲劳与流变学有关，根据流变学我们可以区分多孔弹性疲劳、粘弹性疲劳和弹塑性疲劳。许多水凝胶具有充当增韧剂的牺牲键。我们区分两种类型的增韧剂，根据他们的应力松弛行为下，一个长期的静态拉伸。液态增韧剂松弛至零应力，既不提高静态疲劳门槛值，也不提高循环疲劳门槛值。类固体增韧剂松弛到非零应力，提高静态疲劳门槛值，但不提高循环疲劳门槛值。我们概述了一种策略，以创建高耐久性的水凝胶。由于水凝胶的分子多样性，疲劳的化学性质是发现水凝胶的关键，而水凝胶的性质以前是无法想象的。希望这篇评论有助于连接化学家和机械师。
Hydrogels have been developed since the 1960s for applications in personal care, medicine, and engineering. Evidence has accumulated that hydrogels under prolonged loads suffer fatigue. Symptoms include change in properties, as well as nucleation and growth of cracks. This article is the first review on the fatigue of hydrogels. Emphasis is placed on the chemistry of fatigue-concepts and experiments that link symptoms of fatigue to processes of molecules. Symptoms of fatigue are characterized by testing samples with and without precut cracks, subject to prolonged static and cyclic loads. We describe the use of energy release rate for samples with precut cracks, under the conditions of large-scale inelasticity, for hydrogels of complex rheology. Highlighted are three experimental setups: pure shear, tear, and peel, where energy release rate is readily obtained for materials of arbitrary rheology. We describe chemistries of bonds and topologies of networks. Noncovalent bonds and some covalent bonds are reversible: they reform after breaking under relevant conditions. Most covalent bonds are irreversible. Each topology of networks is a way to connect reversible and irreversible bonds. We review experimental data of hydrogels of five representative topologies of networks. We compare the Lake-Thomas threshold, the cyclic-fatigue threshold, and the static-fatigue threshold. Fatigue is a molecular disease. All symptoms of fatigue originate from one fundamental cause: molecular units of a hydrogel change neighbors under prolonged loads. Fatigue correlates with rheology, according to which we distinguish poroelastic fatigue, viscoelastic fatigue, and elastic-plastic fatigue. Many hydrogels have sacrificial bonds that act as tougheners. We distinguish tougheners of two types according to their stress-relaxation behavior under a prolonged static stretch. A liquid-like toughener relaxes to zero stress, and increases neither static-fatigue threshold nor cyclic fatigue threshold. A solid-like toughener relaxes to a nonzero stress, increases static-fatigue threshold, but does not increase cyclic-fatigue threshold. We outline a strategy to create hydrogels of high endurance. Because of the molecular diversity among hydrogels, the chemistry of fatigue holds the key to the discovery of hydrogels of properties previously unimagined. It is hoped that this review helps to connect chemists and mechanicians.