80/40分钟讲解/答疑30个提问。 视频链接： https://www.koushare.com/video/videodetail/8926 从耦合氫鍵（O:H-O）分段长度、能量、比热非对称受激协同弛豫和极化的角度出发理解水的结构以及诸如浮冰、复冰、润滑、超流、水桥、过热过冷、热水速冷、电致相变等现象的起因反直觉物性是一个令人兴奋而不能自拔的尝试。

views: 92 Month views: 92

The label: Science

Released on December 14, 2020

Changqing Sun

多尺度计算的核心问题是不同尺度模型之间的信息传递，其中以“自上而下”方向的传递最具挑战性，即：宏观连续体在确定的应力状态下，对应微观尺度的原子体系的运动状态如何？由于连续体应力应变和微观原子运动等物理信息存在本质差异，“自上而下”传递的问题长期没有得到较好的解决。借鉴Andersen-Parrinello-Rahman 在分子模拟中控制应力的思想，并在原子体系中引入连续介质微态模型，我们建立了多尺度微态分子动力学理论体系。相比于传统多尺度计算方法“握手”的信息传递方式，微态分子动力学适用于传递复杂、非均匀信息。本报告介绍了微态分子动力学理论体系和计算模型，并讨论了该理论在相变、波的跨尺度传播、动态裂纹跨尺度扩展等方面的应用，以及未来发展方向。

views: 119 Month views: 119

The label: Science,Engineering,Solid mechanics,Material science

Released on November 29, 2020

Qi Tong

High-performance mechanical energy absorption has been pursued to protect personnel and important infrastructures and devices. In this talk, I will introduce our work on the mechanical energy absorption leveraging the liquid intrusion of Metal-Organic-Frameworks (MOFs). It is found that during the intrusion of non-wetting liquids into the nanoscale pores under mechanical pressure, substantial mechanical energy can be absorbed by generating huge liquid-solid interfaces. Some latest research on its physical mechanism and potential engineering applications will be presented.

views: 134 Month views: 134

The label: Science,Engineering,Material science

Released on November 27, 2020

Yueting Sun

挠曲电效应是一种广泛存在于所有介电材料中的力电耦合效应。与压电效应不同，挠曲电效应可以实现材料中应变梯度和电极化的耦合。利用挠曲电效应，我们不仅可以在普通介电材料中实现双向力电耦合，而且能达到直接表征非均匀应变场的目的。本报告从物理、力学及材料等方面介绍了材料中挠曲电效应的提升策略及机制，并阐述了挠曲电效应在俘能及传感等领域的独特应用。

views: 219 Month views: 219

The label: Solid mechanics,Science,Material science

Released on November 13, 2020

Qian Deng

The manufacture of 3D mesostructures is receiving rapidly increasing attention, because of the fundamental significance and practical applications across wide-ranging areas. The recently developed approach of buckling-guided assembly allows deterministic formation of complex 3D mesostructures in a broad set of functional materials, with feature sizes spanning nanoscale to centimeter-scale. Previous studies mostly exploited mechanically controlled assembly platforms using elastomer substrates, which limits the capabilities to achieve on-demand local assembly, and to reshape assembled mesostructures into distinct 3D configurations. This work introduces a set of design concepts and assembly strategies to utilize dielectric elastomer actuators as powerful platforms for the electro-mechanically controlled 3D assembly. Capabilities of sequential, local loading with desired strain distributions allow access to precisely tailored 3D mesostructures that can be reshaped into distinct geometries, as demonstrated by experimental and theoretical studies of ∼30 examples. A reconfigurable inductive–capacitive radio-frequency circuit consisting of morphable 3D capacitors serves as an application example.

views: 71 Month views: 71

The label: Solid mechanics,Material science,Science

Released on November 11, 2020

Wenbo Pang

Many materials are anisotropic. However, there is no widely accepted measure for characterizing the degree of elastic anisotropy. Here, assuming that the limiting case of extreme anisotropy should possess a positive semidefinite stiffness matrix, we propose three criteria to evaluate measures of anisotropy and show that the existing measures in the literature do not satisfy all of the proposed criteria.We then introduce a new measure of anisotropy based on the maximum strain energy ratio that is universally applicable to all material systems. The proposed measure is helpful for understanding the properties and behaviors of materials. Furthermore, this measure can be easily generalized to situations involving multiple fields and nonlinearity. The J-integral based criterion is widely used in elastic-plastic fracture mechanics. However, it is not rigorously applicable when plastic unloading appears during crack propagation. One difficulty is that the energy density with plastic unloading in the J-integral cannot be defined unambiguously. In this paper, we alternatively start from the analysis on the power balance, and propose a surface-forming energy release rate (ERR), which represents the energy available for separating the crack surfaces during the crack propagation and excludes the loading-mode-dependent plastic dissipation. Therefore the surface-forming ERR based fracture criterion has wider applicability, including elastic-plastic crack propagation problems. Several formulae are derived for calculating the surface-forming ERR, and the definition of the energy density or work density is avoided. For any fracture behaviours, the surface-forming ERR is proven to be path-independent. The physical meanings and applicability of the proposed surface-forming ERR, the local ERR, the traditional global ERR, and J-integral are compared and discussed.

views: 217 Month views: 217

The label: Science,Engineering,Solid mechanics

Released on October 21, 2020

Bin Liu

通过分子动力学模拟方法，对离子液体的界面结构与传热过程进行了较为系统的研究。首先基于限域离子液体振动谱演化，揭示了其固液结构转变的内在机制；然后对比范德华及静电作用，初步阐明了离子液体固体界面的微观传热机理，相关的研究成果可以为受限离子液体在相变储能，热量耗散等多个过程提供参考。

views: 141 Month views: 141

The label: Science,Solid mechanics

Released on September 29, 2020

Yanlei Wang

细胞对外界微环境的力学响应主要通过细胞骨架来实现，而细胞骨架的动力学行为使其具有高度的复杂性。研究细胞骨架的力学行为，有助于人们更好地认知和了解细胞的生理学和病理学功能。针对细胞骨架参与的几个细胞力学问题，进行了相关理论建模、分子模拟和有限元模拟。研究的几个问题和主要方法为：（1）建立张拉整体模型，研究在不同加载方式（静态或循环）、不同基底刚度上的极性细胞取向问题。结果表明：细胞骨架的横向支撑部分对细胞取向有重要作用；细胞方位的分布宽度反比于加载幅值等。（2）发展张拉整体模型，探讨单个细胞骨架与群体细胞骨架弹性模量之间的关系，发现群体细胞骨架的弹性模量远高于单细胞的弹性模量，这一结果主要是由于群体细胞中细胞骨架的几何旋转受到了抑制。（3）针对现有AFM压痕实验中发现的细胞骨架弹性模量依赖于压入深度，进行了量纲分析和有限元模拟，得到了一个半定量的压力与压入深度的解析关系。在考虑细胞膜和皮质层表面张力的作用下，我们的解析关系表明：细胞骨架的弹性模量是一个常数，与AFM压入深度无关。相关的理论和模拟结果与大量的实验数据相吻合。

views: 170 Month views: 170

The label: Solid mechanics,Science

Released on September 22, 2020

Guang-Kui Xu

Cell dynamics is of crucial significance for the morphogenesis, self-repair, and other physiological and pathological processes of tissues. Collective cells exhibit greatly different dynamic behaviors from isolated cells. In this lecture, some recent advances in experimental and theoretical researches on collective cell dynamics will be presented, with particular attention paid to the biomechanical mechanisms underlying the morphodynamics of developing embryos and tumors. First, a cell division model is established for the division of interconnecting cells in a biological tissue. Coupled mechanical-chemical mechanisms involved in the multi-phase cell division are taken into account. Second, we explain why spontaneous oscillation of collective cells may occur in such biological tissues as Drosophila amnioserosa during development. It is revealed that the collective cell oscillation in an epithelium-like monolayer results from the dynamic bifurcation induced by feedback between mechanical strains and chemical cues. Further, we investigate, both experimentally and theoretically, the migration of collective cells. We show that migratory cells may behave as a whole either like a viscous solid or fluid, leading to rich patterns with characteristic sizes ranging from several to dozens of cells. On the basis of experimental measurements and theoretical analysis, universal statistical laws are derived for the dynamic features of collective cells.

views: 216 Month views: 216

The label: Science

Released on September 17, 2020

Xi-Qiao Feng

凭借超越天然材料的超常物理性能与波动控制特性，超材料与超表面已发展成为具有重要工程应用价值和广泛应用前景的热点前沿领域。与电磁波和声波相比，弹性波具有更多模态特征，会产生更复杂的散射特性，为超材料/超表面的弹性波控制提出更多挑战。本报告将围绕几种弹性超材料与超表面的结构设计，着重介绍我们关于其在波阵面重塑、非对称传播及隔振“牢笼”等弹性波控制方面的研究。

views: 177 Month views: 177

The label: Science,Engineering,Solid mechanics

Released on September 16, 2020

Bing Li