We theoretically explain the complete sequence of shapes of deflated spherical shells. Decreasing the volume, the shell remains spherical initially, then undergoes the classical buckling instability, where an axisymmetric dimple appears, and, finally, loses its axisymmetry by wrinkles developing in the vicinity of the dimple edge in a secondary buckling transition. We describe the first axisymmetric buckling transition by numerical integration of the complete set of shape equations and an approximate analytic model due to Pogorelov. In the buckled shape, both approaches exhibit a locally compressive hoop stress in a region where experiments and simulations show the development of polygonal wrinkles, along the dimple edge. In a simplified model based on the stability equations of shallow shells, a critical value for the compressive hoop stress is derived, for which the compressed circumferential fibres will buckle out of their circular shape in order to release the compression. By applying this wrinkling criterion to the solutions of the axisymmetric models, we can calculate the critical volume for the secondary buckling transition. Using the Pogorelov approach, we also obtain an analytical expression for the critical volume at the secondary buckling transition: The critical volume difference scales linearly with the bending stiffness, whereas the critical volume reduction at the classical axisymmetric buckling transition scales with the square root of the bending stiffness. These results are confirmed by another stability analysis in the framework of Donnel, Mushtari and Vlasov (DMV) shell theory, and by numerical simulations available in the literature.
Buckling of thermally fluctuating spherical shells: Parameter renormalization and thermally activated barrier crossing
研究了热涨落对球形静止弹性薄胶囊屈曲行为的影响。热涨落通过两种机制影响屈曲不稳定性。一方面，由于不同波长的法向位移模式之间的非谐耦合，热波动可以使胶囊的弹性性质和压力重新归一化。这有效地降低了其临界屈曲压力[Kosmrlj and Nelson，Phys. Rev. X 7，011002（2017）]。另一方面，屈曲形状在低于经典屈曲压力的压力下已经是能量有利的。然而，在这些压力下，屈曲需要克服一个能量势垒，它只在临界屈曲压力下消失。在存在热波动的情况下，胶囊可以通过已经在低于临界屈曲压力的压力下的热激活自发地克服热能量级的能量势垒。我们重温参数重整化的热涨落和制定的屈曲准则的基础上尺度相关的重整化参数，以获得温度依赖的临界屈曲压力。然后，我们量化的压力依赖的能量障碍屈曲临界屈曲压力以下，使用数值能量最小化和分析参数。这使我们能够获得依赖于温度的临界压力屈曲的热激活超过这个能量障碍。最后，我们研究了参数重整化和热激活的组合效应，通过使用重整化参数的能量势垒的热激活，得到了我们的最终结果的温度依赖的临界压力，这是显着低于结果，如果只考虑参数重整化或只考虑热激活。
Electro-mechanical wrinkling of soft dielectric films bonded to hyperelastic substrates
Zhejiang University（浙江大学）；University of Galway（戈尔韦大学）；Center for Soft Machines and Smart Devices, Huanjiang Laboratory（软机器与智能设备中心，环江实验室）；Ningbo University（宁波大学）；SISSA – International School for Advanced Studies（SISSA-高级研究国际学校）
Nonreciprocal buckling makes active filaments polyfunctional
School of Physics, UNSW（新南威尔士大学物理学院）；ARC Centre of Excellence for the Mathematical Analysis of Cellular Systems - UNSW Node（澳大利亚研究委员会细胞系统数学分析卓越中心-新南威尔士大学节点）；Department of Mathematics, Faculty of Mathematics and Natural Sciences, University of Oslo（奥斯陆大学数学与自然科学院数学系）；Institute of Physics, Universiteit van Amsterdam（阿姆斯特丹大学物理研究所）；TCM Group, Cavendish Laboratory, University of Cambridge（剑桥大学卡文迪许实验室理论凝聚态物理组）
