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Robustness of structural superlubricity beyond rigid models

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Friction 2022年第9期10卷 1382-1392页

作者： Shizhe FENG Zhiping XU applied mechanics Laboratory Department of Engineering Mechanics and Center for Nano and Micro MechanicsTsinghua UniversityBeijing 100084China

Structural superlubricity is a theoretical concept stating that the friction force is absent between two rigid,incommensurate crystalline surfaces.However,elasticity of the contact pairs could modify the lattice registry at interfaces by nucleating local slips,favoring commeasure.The validity of structural superlubricity is thus concerned for large-scale systems where the energy cost of elastic distortion to break the lattice registry is low.In this work,we study the size dependence of superlubricity between single-crystal graphite flakes.Molecular dynamics simulations show that with nucleation and propagation of out-of-plane dislocations and strained solitons at Bernal interfaces,the friction force is reduced by one order of magnitude.Elastic distortion is much weaker for non-Bernal or incommensurate ones,remaining notable only at the ends of contact.Lattice self-organization at small twist angles perturbs the state of structural superlubricity through a reconstructed potential energy surface.Theoretical models are developed to illustrate and predict the interfacial elastoplastic behaviors at length scales beyond those in the simulations.These results validate the rigid assumption for graphitic superlubricity systems at microscale,and reveal the intrinsic channels of mechanical energy dissipation.The understandings lay the ground for the design of structural superlubricity applications.

关键词： structural superlubricity lattice registry elastic deformation strained solitons crystal plasticity molecular dynamics simulations

硬/软复合材料结构防爆性能的实验及数值评估

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Acta Mechanica Sinica 2022年第1期38卷 27-36页

作者：杨丰源栗志杰庄茁柳占立 applied mechanics Laboratory Department of Engineering MechanicsSchool of AerospaceTsinghua UniversityBeijing 100084China

现实防护工程中,硬1软复合结构在人员装甲(如头盔的外壳/衬里系统)中的应用可以有效减轻爆炸伤害.由于缺乏有效可靠的实验方法评估防护结构的防爆性能,直接接触型防护结构的发展受到限制,本文针对硬/软复合材料结构的防爆性能测试提出... 详细信息

现实防护工程中,硬1软复合结构在人员装甲(如头盔的外壳/衬里系统)中的应用可以有效减轻爆炸伤害.由于缺乏有效可靠的实验方法评估防护结构的防爆性能,直接接触型防护结构的发展受到限制,本文针对硬/软复合材料结构的防爆性能测试提出一种新的实验及数值评估方法,并对其防爆机理进行了分析.受测的硬/软结构由超高分子量聚乙烯(UHMWPE)复合材料和膨胀聚乙烯(EPE)泡沫组成.现场爆炸试验通过7.0 kg TNT球形炸药在3.8 m处产生的爆炸波来完成.设计了一种压力测试装置用于支撑被测结构并测量穿透防护结构的爆炸压力脉冲.实验结果表明,通过使脉冲波形更平坦、减小压力幅度和延迟脉冲到达时间,硬/软结构可以将爆炸压力脉冲减弱为三角形压力脉冲.7mmUHMWPE复合材料和20mmEPE泡沫的组合防护结构可将爆炸压力振幅降低40%.通过有限元模拟分析爆炸缓解机制.数值结果表明,爆炸压力脉冲的衰减主要发生在硬/软界面上,通过界面反射压力波和软材料层变形吸收动能来完成.在此基础上提出的理论模型可以很好地解释实验和数值结果,对评价和设计高性能的防爆结构具有重要意义.

关键词：防爆结构防爆性能接触型压力脉冲复合材料结构脉冲到达时间爆炸试验复合结构

Analysis and design for the comprehensive ballistic and blast resistance of polyurea-coated steel plate

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Defence Technology（防务技术） 2023年第1期19卷 35-51页

作者： Dongyang Chu Yigang Wang Shanglin Yang Zhijie Li Zhuo Zhuang Zhanli Liu applied mechanics Laboratory Department of Engineering MechanicsSchool of Aerospace EngineeringTsinghua UniversityBeijing100084China

Fragments and blast waves generated by explosions pose a serious threat to protective structures.In this paper,the impact resistance of polyurea-coated steel plate under complex dynamic loading is analyzed and designed for improving comprehensive ballistic and blast resistance using the newly established computational evaluating model.Firstly,according to the thickness and placement effects of the coating on the impact resistance,the steel-core sandwich plates are designed,which are proved to own outstanding comprehensive ballistic and blast resistance.Besides,the distribution diagram of ballistic and blast resistance for different polyurea-coated steel plates is given to guide the design of protective structures applying in different explosion scenarios.Furthermore,the dynamic response of designed plates under two scenarios with combined fragments and blast loading is studied.The results show that the synergistic effect of the combined loading reduces both the ballistic and blast resistance of the polyurea-coated steel plate.Besides,the acting sequence of the fragments and blast affects the structural protective performance heavily.It is found that the first loading inducing structural large deformation or damage is dominant.When fragments impact first,the excellent unit-thickness ballistic performance of the structural front part is strongly needed for improving the comprehensive ballistic and blast resistance.

关键词： Polyurea Ballistic and blast resistance Combined fragments and blast loading

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管状上皮组织的三维形态发生

Acta Mechanica Sinica 2024年第2期40卷 237-243页

作者：于鹏宇李博 Institute of Biomechanics and Medical Engineering Applied Mechanics LaboratoryDepartment of Engineering MechanicsTsinghua UniversityBeijing100084China

管状上皮组织是组成多种器官的基本结构,其形态发生涉及到细胞变形、生化信号转导,以及细胞之间和细胞与细胞外基质之间的相互作用.目前尚未完全清楚力学和生化信号之间的相互作用如何调节该形态学过程.本文构建了耦合生化信号通路的三... 详细信息

管状上皮组织是组成多种器官的基本结构,其形态发生涉及到细胞变形、生化信号转导,以及细胞之间和细胞与细胞外基质之间的相互作用.目前尚未完全清楚力学和生化信号之间的相互作用如何调节该形态学过程.本文构建了耦合生化信号通路的三维细胞顶点模型,用于探究管状组织的形态发生.数值计算结果表明管腔尺寸受到细胞和细胞外基质的力学性质的影响,且细胞的力学-化学耦合的变形可以激发斑点状和条带状的超细胞肌动球蛋白斑图,进而介导组织形成波浪形和竹节形的管腔结构,该过程会受到化学扩散强度的调节.本研究突显了力学-化学相互作用在生物组织形态动力学中的重要作用,并且提供了一个三维计算框架以深入理解生命系统中复杂的斑图形成过程.

关键词：化学相互作用细胞变形肌动球蛋白形态发生管状组织细胞外基质三维形态波浪形

Effect of interactions of two holes on tensile behavior of patch repaired carbon/epoxy woven laminates

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Defence Technology（防务技术） 2023年第3期21卷 88-93页

作者： Gursahib Singh Bhatia Arockiarajan A. Department of Applied Mechanics Indian Institute of Technology Madras600036ChennaiIndia

The conventional case of patch repair involves bonding a patch over single damage/hole in the laminate.This work investigates the effect of interaction of two holes on the tensile behavior patch repaired carbon epoxy woven laminates.The specimens of[0°/45°/45°/0°]laminates were repaired with adhesively bonded two-ply[45°]2external patches.Three different cases of drilled specimens were produced with different hole arrangements viz.specimens with single central hole(SH),with two holes aligned along the longitudinal axis(LH)and with two holes along transverse axis(TH).The two-hole specimens were repaired with two different types,i.***.single large patches(SP)and with the two smaller patches(DP)of combined bonding area equal to the single large patches.Digital image correlation(DIC)was employed to capture strain contours.The results reveal the difference in the load transfer through the patches depending upon the arrangement of holes.The TH repaired specimen exhibit significant load recovery(SP-32.75%,DP-34.62%)while the LH specimens result in very marginal(SP-6.11%,DP-4.10%)recovery compared to their drilled case.The TH specimen failed by crack growing through both the holes beneath the patch,while the LH specimens failed by the failure through only one hole.The use of single large patch over multiple holes and multiple small patches individually over each hole has no significant influence on load recovery.

关键词： crack patch behavior

Crashworthiness Design and Multi-Objective Optimization of Bionic Thin-Walled Hybrid Tube Structures

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Computer Modeling in Engineering & Sciences 2024年第4期139卷 999-1016页

作者： Pingfan Li Jiumei Xiao Department of Applied Mechanics University of Sciences and Technology BeijingBeijing100083China

Thin-walled structures are widely used in cars due to their lightweight construction and energy-absorbing properties.However,issues such as high initial stress and lowenergy-absorbing efficiency arise.This study proposes a novel energy-absorbing structure inwhich a straight tube is combinedwith a conical tube and a bamboo-inspired bulkhead structure is introduced.This configuration allows the conical tube to flip outward first and then fold together with the straight tube.This deformation mode absorbs more energy and less peak force than the conical tube sinking and flipping inward.Through finite element numerical simulation,the specific energy absorption capacity of the structure is increased by 26%compared to that of a regular circular cross-section tube.Finally,the impact resistance of the bionic straight tapered tube structure is further improved through multi-objective optimization,promoting the engineering application and lightweight design of hybrid cross-section tubes.

关键词： Crashworthiness tube inversion multi-objective optimization energy absorption

Investigation on nonlinear multi-scale effects of unsteady flow in hydraulic fractured horizontal shale gas wells

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applied Mathematics and mechanics(English Edition) 2018年第2期39卷 181-192页

作者： Jiaxuan LIU Xinchun SHANG Weiyao ZHU Department of Applied Mechanics University of Science and Technology Beijing Institute of applied mechanics University of Science and Technology Beijing

A unified mathematical model is established to simulate the nonlinear unsteady percolation of shale gas with the consideration of the nonlinear multi-scale effects such as slippage, diffusion, and desorption. The continuous inhomogeneous models of equivalent porosity and permeability are proposed for the whole shale gas reservoir includ- ing the hydraulic fracture, the micro-fracture, and the matrix regions. The corresponding semi-analytical method is developed by transforming the nonlinear partial differential governing equation into the integral equation and the numerical discretization. The nonlinear multi-scale effects of slippage and diffusion and the pressure dependent effect of desorption on the shale gas production are investigated.

关键词： shale gas nonlinear effect multi-scale percolation inhomogeneous perme ability integral equation

Dispersed multiphase flows:advances in measuring,simulation and modeling

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Acta Mechanica Sinica 2022年第8期38卷 1-3页

作者： Cristian Marchioli Lihao Zhao department of Engineering and Architecture University of UdineUdine33100Italy Key Laboratory of applied mechanics Department of Engineering MechanicsTsinghua UniversityBeijing100084China

Dispersed multiphase flows are commonly encountered in a wide variety of natural and industrial applications,from sedimentation in rivers and plankton surfacing in oceanic flows to fluidized bed in chemical reactors and pneumatic conveying systems.In these flows,a dispersed phase(con-sisting of particles,droplets and/or bubbles)is transported by a carrier phase.The interaction between the phases re-sults in complex dynamics(e.g.,transport,spatial clustering,and deformation or break-up)that is rich in physics and poses a wide spectrum of theoretical,computational,and experimental challenges.These challenges are at the very core of the research efforts made by the multiphase flow community over the past decades.

关键词： multiphase flows dispersed

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湍流中的趋旋性主动粒子研究进展

Acta Mechanica Sinica 2022年第8期38卷 4-17页

作者：邱敬然 Cristian Marchioi 赵立豪 Key Laboratory of applied mechanics Department of Engineering MechanicsTsinghua UniversityBeijing100084China department of Engineering and Architecture University of UdineUdine33100Italy

许多海洋浮游生物能够主动运动.它们会在昼夜间进行垂向的迁徙,穿过数十米高的水层.微小的浮游生物是如何在湍流环境中实现定向迁移的呢?趋旋稳定性是其中一种机制,其表现为浮游生物在重力作用下倾向于沿着特定方向游动.由于特定机制,... 详细信息

许多海洋浮游生物能够主动运动.它们会在昼夜间进行垂向的迁徙,穿过数十米高的水层.微小的浮游生物是如何在湍流环境中实现定向迁移的呢?趋旋稳定性是其中一种机制,其表现为浮游生物在重力作用下倾向于沿着特定方向游动.由于特定机制,如细胞的质量非均匀分布,许多浮游生物受到一种由重力引起的力矩,使其面朝重力的反方向游动.然而,其游动方向往往会被海洋湍流中的剪切和速度脉动扰乱:这些扰动产生的黏性力矩会让浮游生物的游动方向失稳.在重力力矩和黏性力矩的共同作用下,浮游生物朝特定方向的运动特性便被称为趋旋性.人们发现这一机制能够导致浮游生物的非均匀分布,使它们形成团簇或者薄层.这些现象由流体运动引起的非线性动力学过程决定,而这一领域的研究正吸引越来越多的关注.将Navier-Stokes方程的与趋旋游动粒子的模型方程结合的数值模拟方法受到广泛使用,并展现出其潜力.该方法能够让人们能够深入研究自推进粒子的动力学和统计学性质.在本文中,我们对湍流中趋旋粒子的近期关键进展进行了综述.首先,我们介绍了关于趋旋粒子的朝向和它们垂向迁移的相关研究.其次,我们讨论了关于趋旋粒子聚集性的研究.最后,我们回顾了壁湍流中的趋旋粒子运动行为的相关研究.

关键词：海洋浮游生物特定方向非均匀分布流体运动定向迁移非线性动力学速度脉动模型方程