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Unusual stress and strain concentration behaviors at the circular hole of a large monodomain liquid crystal elastomer sheet
Journal of the Mechanics and Physics of Solids ( IF 5.0 ) Pub Date : 2021-08-15 , DOI: 10.1016/j.jmps.2021.104615
Yuefeng Jiang 1 , Lihua Jin 2 , Yongzhong Huo 1
Affiliation  

Liquid crystal elastomers combine the hyperelasticity of elastomers with the multi-functionality of liquid crystals and have emerged as an important class of soft active materials. Monodomain liquid crystal elastomers under loading exhibit the soft elastic behavior due to the stress induced director rotation and the resulting spontaneous strain. Here, we numerically study their stress and strain concentration behavior by considering the classical example, a large sheet with a small circular hole in the middle under uniaxial loading. The concentration behavior is found to be very different from regular elastomers. Firstly, the concentration factors are much bigger at both small and large strains. Secondly, the locations of the strain concentration may not coincide with that of the stress concentration. Detailed analysis of the director rotation and the resulting spontaneous strain around the free edge of the hole are shown to be the main causes for the unusual concentration behavior. Moreover, under a given strain, the stress level of the LCE sample, and therefore the free energy, is slightly lower than that of the neo-Hookean material, while the local free energy density on the hole edge is much bigger due to the severer concentrations. By considering material parameters obtained from various samples of polysiloxane and polyacrylate side-chain nematic elastomers, we find that their stress and strain concentration behaviors are qualitatively similar but quantitatively quite different. As a result, at a prescribed strain, the samples with a larger maximal spontaneous strain has severer stress and strain concentrations. The stress concentration factor difference scaled by a coupling constant that combines the effect of the two material parameters, r and a, increases as the semi-soft coefficient a decreases. Similar results are found for the scaled maximal spontaneous strains and the scaled strain concentration factor difference at small strains.



中文翻译:

大型单畴液晶弹性体片圆孔处的异常应力和应变集中行为

液晶弹性体结合了弹性体的超弹性和液晶的多功能性,已成为一类重要的软活性材料。由于应力引起的指向矢旋转和由此产生的自发应变,负载下的单畴液晶弹性体表现出软弹性行为。在这里,我们通过考虑经典示例,在单轴加载下中间带有小圆孔的大板,对它们的应力和应变集中行为进行了数值研究。发现浓度行为与常规弹性体非常不同。首先,无论是小应变还是大应变,浓度因子都大得多。其次,应变集中的位置可能与应力集中的位置不一致。对导向器旋转的详细分析和由此产生的孔自由边缘周围的自发应变被证明是异常集中行为的主要原因。此外,在给定的应变下,LCE 样品的应力水平,因此自由能,略低于新胡克材料,而孔边缘的局部自由能密度由于更严格而大得多。浓度。通过考虑从聚硅氧烷和聚丙烯酸酯侧链向列弹性体的各种样品获得的材料参数,我们发现它们的应力和应变集中行为在质量上相似但在数量上却大不相同。因此,在规定的应变下,最大自发应变较大的样品具有更严重的应力和应变集中。ra随半软系数a 的减小而增加。对于按比例缩放的最大自发应变和在小应变处按比例缩放的应变集中因子差异,发现了类似的结果。

更新日期:2021-08-26
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