复习:疲劳水凝胶

这是我们关于水凝胶疲劳的综述文章。这是对这门学科的第一次回顾。我们认为疲劳是材料在长时间静载荷或循环载荷下的任何失效。本文从基础开始，涵盖了广泛的领域，但留下了许多有趣的问题有待回答。本文将水凝胶的化学性质与力学性质联系起来。

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https://www.sciencedirect.com/science/article/pii/S0997753818309203?dgci..。

水凝胶疲劳

白若冰，杨佳伟，索志刚*

摘要

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。越来越多的证据表明，水凝胶在长时间负荷下会产生疲劳。症状包括性质的改变，以及裂纹的成核和增长。本文是对水凝胶疲劳研究的首次综述。重点放在疲劳的化学概念和实验，将疲劳的症状与分子的过程联系起来。疲劳症状的特点是测试样品有和没有预切割裂纹，受到长期的静态和循环载荷。我们描述了在大尺度非弹性条件下，对于复杂流变的水凝胶，使用具有预切裂缝的样品的能量释放率。强调了三个实验设置:纯剪切，撕裂和剥离，其中能量释放率很容易获得任意流变的材料。我们描述化学键和网络的拓扑结构。非共价键和部分共价键是可逆的:它们在一定条件下断裂后重新形成。 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.