Exceptional stress-director coupling at the crack tip of a liquid crystal elastomer
Exceptional stress-director coupling at the crack tip of a liquid crystal elastomer
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DOI：
10.1016/j.jmps.2023.105522
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发表时间：
2023-12
影响因子：
5.3
通讯作者：
Chen Wei;Yu Zhou;Benny Hsu;L. Jin
中科院分区：
文献类型：
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作者：
Chen Wei;Yu Zhou;Benny Hsu;L. Jin
液晶弹性体（LCE）是一种含有棒状液晶的特殊弹性体，这些液晶沿一定方向排列，称为指向矢。LCE的指向矢可以在应力下旋转，导致大的自发应变和软弹性行为。这项研究揭示了如何在一个单畴LCE强应力导向耦合诱导独特的裂纹尖端场和断裂行为。通过拉伸具有不同初始指向矢的边裂纹LCE，我们从理论和实验上描述了位移场和指向矢场。结果表明，董事进行显着的和不均匀的旋转裂纹尖端，导致非常不同的应力/应变分布从传统的弹性体。特别是当初始指向矢与加载方向倾斜时，裂纹面附近的应力应变分布是不对称的。值得注意的是，我们发现一个畴壁形成沿着一定的极角在裂纹尖端，与相反的指向矢旋转，从而剪切应变，在畴壁的两侧。此外，LCEs与倾斜的初始董事的负载表现出更小的裂纹开口和能量释放率比那些新胡克材料，而LCEs与平行董事表现出更高的值。我们将这些发现归因于远程区域的体软化和裂纹尖端附近形成的相反指向矢旋转域的综合效应。这项研究提供了一个了解LCEs的应力导向耦合如何触发其独特的裂纹尖端领域，并深入了解战略，以提高LCEs的断裂性能，为未来的应用。
A liquid crystal elastomer (LCE) is a special elastomer containing rod-like liquid crystals, which align in a certain direction, called the director. The director of a LCE can rotate under stress, resulting in large spontaneous strain and soft elastic behavior. This study unravels how the strong stress-director coupling in a monodomain LCE induces unique crack-tip fields and fracture behavior. Through stretching edge-cracked LCEs with various initial directors, we characterize the displacement and director fields theoretically and experimentally. The results reveal that the directors undergo significant and inhomogeneous rotation at the crack tips, leading to very different stress/strain distributions from traditional elastomers. Particularly, when the initial director is tilted to the loading direction, the stress/strain distributions are asymmetrical about the crack plane. Notably, we discover a domain wall forms along a certain polar angle at the crack tip, with opposite director rotation, and thereby shear strain, on the two sides of the domain wall. Moreover, LCEs with a tilted initial director to the loading exhibit much smaller crack openings and energy release rates than those of neo-Hookean materials, while LCEs with a parallel director exhibit higher values. We attribute these findings to a combined effect of bulk softening at the remote region and the formation of domains of opposite director rotation near the crack tip. This study provides an understanding of how the stress-director coupling of LCEs triggers their unique crack-tip fields, and insights into strategies to enhance the fracture properties of LCEs for future applications.