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水中荷叶为何形貌各异?

荷叶表面微结构超疏水现象曾引起科研人员的广泛关注,而荷叶生长的形貌演变也同样有趣:漂浮在水面上的荷叶边缘通常会出现短波褶皱,而生长在水面之上的荷叶则表现为整体弯曲的锥形并在边缘处出现长波褶皱。是什么原因导致了伫立水上和漂浮在水面的同种荷叶的形貌差异呢?为理解这一现象背后的力学机理,我们建立了能够有效解释漂浮叶片和悬空叶片的各向异性微分生长薄板模型,可解释多种水生植物形态各异的原因,并定量预测形貌形成与演化全景。另外,我们发现茎/脉约束、非均匀生长引起的曲率和尺寸效应等因素对生长形貌有重要影响。更进一步,受自然启发,通过吸水橡胶膨胀仿生实验再现了自然界中多种几何构型(圆形、扇形和矩形)和生长方式(整体、局部和边缘膨胀)的水生植物的形貌。研究结果不仅对多种水生植物生长形貌的发生发展提供了科学的解释,也提出了通过基底或边缘驱动表面失稳来实现仿生可展结构形貌控制的新思路。

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Fan Xu
  • Video language: Chinese
  • Related paper #1
  • Journal name: Physical Review Letters
  • Periodical year: 2020
  • Authors: Fan Xu, Chenbo Fu, Yifan Yang
  • Doi: http://dx.doi.org/10.1103/PhysRevLett.124.038003
  • Related paper #2
  • Journal name: Physics
  • Periodical year: 2020
  • Authors: Peter Weiss
  • Doi: https://physics.aps.org/articles/v13/8
  • Related paper #3
  • Journal name: Nature
  • Periodical year: 2020
  • Authors: Mark Zastrow
  • Doi: https://www.nature.com/articles/d41586-020-00189-z
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Curvature tunes wrinkles in tensile hyperelastic shells

Transverse wrinkles usually occur in a uniaxially tensile elastic membrane and will be smoothed upon excess stretching. This instability-restabilization response (isola-center bifurcation) can originate from the nonlinear competition between stretching energy and bending energy. Here, we find a crucial factor, the curvature, which can control effectively and precisely the wrinkling and smoothing regimes. When the sheet is bent with curvature, the regime of wrinkling amplitude versus membrane elongation is narrowed, with local wrinkling instability coupled with global bending. There exists a critical curvature, where no wrinkles appear when the value is beyond this threshold. The curvature effects on wrinkling-smoothing behavior have been quantitatively explored by our theories, computations and experiments. The models developed in this work can describe large in-plane strains of soft shells to effectively capture this transition behavior, which build on general differential geometry and thus can be extended to arbitrary smooth surfaces with varying curvature such as torus. Our findings may shed light on designs of wrinkle-tunable membrane surfaces and structures.

Released on September 08, 2021
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