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Research progress on advanced rail materials for electromagnetic railgun technology

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Defence Technology（防务技术） 2021年第2期17卷 429-439页

作者： Hong-bin xie Hui-ya Yang Jian Yu Ming-yu Gao Jian-dong Shou You-tong Fang Jia-bin Liu Hong-tao Wang School of Materials Science and Engineering Zhejiang UniversityHangzhou310027China center for x-mechanics Faculty of EngineeringZhejiang UniversityHangzhou310027China

Electromagnetic railgun attracts more and more attention due to its advantage in speed,cost,and *** is found that the rail should withstand huge mechanical and thermal shocks during the launching *** forms of rail failure are accompanied by gouge,grooving,transition,and arc ablation,*** service life of the rail has become a bottleneck restricting the development of electromagnetic railgun technology.A series of researches are carried out to solve rail failure,including analysing the failure mechanism and using various advanced rail *** paper provides a comprehensive review of rail materials,including material composition,preparation,microstructure,and *** begin from a short background of the requirement of the rail *** a detailed investigation of rail materials is described,and the performances of those materials are ***,further development prospect of rail material is discussed.

关键词： Strength Conductivity Electromagnetic railgun Copper alloys Rai

Design and analysis of an untethered micro flapping robot which can glide on the water

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Science China(Technological Sciences) 2022年第8期65卷 1749-1759页

作者： CHEN YanHong LIU YiDe LIU TaiShan LI Hua QU Shaoxing YANG Wei State Key Laboratory of Fluid Power&Mechatronic System Key Laboratory of Soft Machines and Smart Devices of Zhejiang ProvincesCenter for X-MechanicsDepartment of Engineering MechanicsZhejiang UniversityHangzhou 310027China

Flapping-wing flying insects possess various advantages,such as high agility and *** design and manufacture of insect-scale flapping-wing micro aerial vehicle(FWMAV)have attracted increasing attention in recent *** to the limitations of size and weight,the FWMAV with an onboard battery which can fully mimic insect flight has not been *** this work,we design and fabricate a highly integrated flapping-wing microrobot named *** Robomoth consists of a carbon chassis,customized power and control devices,and two piezoelectric ceramic actuators symmetrically distributed in the thorax and controlled *** weighs 2.487 g,spans 5.9 cm in length,possesses 9 cm of wingspan,and carries a 0.355 g rechargeable lithium *** demonstrate the mobility of the Robomoth through untethered gliding and making turns on the water surface.A simplified dynamic model of the flapping system is proposed to explain the relationship between the driving frequency and the flapping *** Robomoth is one new untethered bioinspired flapping-wing robot that can perform stable water surface motion,which holds potential applications such as search and rescue on the *** robot can also provide insight for designing insect-scale flying vehicles.

关键词： micro/nanorobots biologically inspired robots flapping-wing flying piezoelectric ceramic actuator

mechanics of flexible and stretchable piezoelectrics for energy harvesting

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Science China(Physics,mechanics & Astronomy) 2015年第9期58卷 39-51页

作者： CHEN Ying LU BingWei OU DaPeng FENG xue Department of Engineering mechanics Tsinghua University center for mechanics and Materials Tsinghua University

As rapid development in wearable/implantable electronic devices benefit human life in daily health monitoring and disease treatment medically, all kinds of flexible and/or stretchable electronic devices are booming, together with which is the demanding of energy supply with similar mechanical property. Due to its ability in converting mechanical energy lying in human body into electric energy, energy harvesters based on piezoelectric materials are promising for applications in wearable/implantable device's energy supply in a renewable, clean and life-long way. Here the mechanics of traditional piezoelectrics in energy harvesting is reviewed, including why piezoelectricity is the choice for minor energy harvesting to power the implantable/wearable electronics and how. Different kinds of up to date flexible piezoelectric devices for energy harvesting are introduced, such as nanogenerators based on Zn O and thin and conformal energy harvester based on PZT. A detailed theoretical model of the flexible thin film energy harvester based on PZT nanoribbons is summarized, together with the in vivo demonstration of energy harvesting by integrating it with swine heart. Then the initial researches on stretchable energy harvesters based on piezoelectric material in wavy or serpentine configuration are introduced as well.

关键词： piezoelectric effect energy harvesting flexible electronics stretchable electronics

Atomistic simulations of martensitic transformation processes for metastable FeMnCoCr high-entropy alloy

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Science China(Technological Sciences) 2023年第4期66卷 998-1006页

作者： WANG Peng LIN YiCheng CAO Yu ZHAO HaoRan LI QianQian WANG HongTao Shanghai Key Laboratory of mechanics in Energy Engineering Shanghai Institute of Applied Mathematics and MechanicsSchool of Mechanics and Engineering ScienceShanghai UniversityShanghai 200444China center for x-mechanics Zhejiang UniversityShanghai 200444China Materials Genome Institute Shanghai UniversityHangzhou 310027China Institute of Applied mechanics Zhejiang UniversityHangzhou 310027China

Non-equiatomic FeMnCoCr high-entropy alloy(HEA),which exhibits a great potential to break the strength-ductility trade-off relationship,has drawn abundant attention from researchers in ***,atomic simulations of such excellent alloys are limited due to the lack of proper interatomic *** this work,the complete martensitic transformation of nonequiatomic HEA is reproduced via atomic simulations with a novel interatomic potential under EAM *** physical parameters of interatomic potential agree well with experimental measurements and first-principles *** to the atomic simulation results of poly-crystalline under tension and compression,two basic transition models of TRIP-DP-HEA for martensitic transformation are revealed,i.e.,the overlapping of intrinsic stacking faults or the growth of hcp laminates ***,the pathway for martensitic transformation is elucidated with the gliding of Shockley partial dislocations of 1/6burgers vectors.

关键词： dual-phase high entropy-alloy molecular dynamics simulation FeMn-steels martensitic transformation

Improving the thermal shock resistance of ceramics by crack arrest blocks

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Science China(Technological Sciences) 2016年第6期59卷 913-919页

作者： WANG Yan Wei xIA Biao SU Hong Hong CHEN Hang FENG xue Applied mechanics Laboratory Department of Engineering Mechanics Tsinghua University center for mechanics and Materials Tsinghua University Department of Engineering mechanics Chongqing University

Ceramics used in the high temperature environment are inevitably subjected to sudden temperature change, which may lead to catastrophic thermal shock failure due to the intrinsic brittleness of ceramics. In this paper, an experimental platform is designed to realize the in-situ observation during the thermal shock experiments. Experimental results show that all the cracks initiate from one of the edge midpoints and propagate to another one for square specimens. Such experimental observation is consistent with the maximum tensile stress zone with the maximum temperature gradient given by the finite element method(FEM). The different crack modes resulting from different heating rates after thermal shock experiments are observed and analyzed. Comparison between different clamping methods is conducted to study the effects of boundary conditions on the thermal shock experiments. Furthermore, in order to improve the thermal shock performance of alumina ceramics, crack arrest blocks are added near the edge midpoint. The thickness, shape and arrangement of the blocks are systematically investigated to understand the mechanism of improvement of thermal shock resistance.

关键词： thermal shock ultra-high temperature ceramics crack arrest blocks in-situ dynamic observation

Analyses of mechanically-assembled 3D spiral mesostructures with applications as tunable inductors

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Science China(Technological Sciences) 2019年第2期62卷 243-251页

作者： ZHANG Fan LIU Fei ZHANG YiHui Key Laboratory of Applied mechanics of Ministry of Education Department of Engineering Mechanics Tsinghua University center for Flexible Electronics Technology and center for mechanics and Materials Tsinghua University

Mechanically-guided assembly allows the formation of 3D spiral-shaped inductors through controlled buckling, which could provide an increased quality(Q) factor and broadened working angle in near field communication, as compared to the planar design. An understanding of the microstructure-property relationship is essential in the design optimization of the assembly process. This work presents a theoretical model to analyze the deformations during the assembly of the 3D spiral-shaped mesostructure from a bilayer precursor that consists of a supporting ribbon and a 2D coil on its top. As validated by both the experiments and finite element analyses(FEA), this mechanics model allows accurate predictions of the assembled 3D configurations. In combination of electromagnetic simulations, we investigated the effects of various key design parameters on the final 3D configuration and the Q factor when operated as an inductor. The results suggest a significant role of the gravity effect on the assembled spiral configuration, especially for flexible coil designs with relative small cross-sectional areas or long *** study can serve as a reference for the design of spiral-shaped 3D inductors in different device applications.

关键词： 3D assembly modeling buckling multilayer tunable inductor

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 ***,elasticity of the contact pairs could modify the lattice registry at interfaces by nucleating local slips,favoring *** validity of structural superlubricity is thus concerned for large-scale systems where the energy cost of elastic distortion to break the lattice registry is *** this work,we study the size dependence of superlubricity between single-crystal graphite *** 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 *** distortion is much weaker for non-Bernal or incommensurate ones,remaining notable only at the ends of *** self-organization at small twist angles perturbs the state of structural superlubricity through a reconstructed potential energy *** models are developed to illustrate and predict the interfacial elastoplastic behaviors at length scales beyond those in the *** results validate the rigid assumption for graphitic superlubricity systems at microscale,and reveal the intrinsic channels of mechanical energy *** 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

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高压热处理调节FeP金属玻璃空化行为

Acta Mechanica Sinica 2023年第3期39卷 198-207页

作者：唐垚周昊飞 center for x-mechanics Department of Engineering MechanicsZhejiang UniversityHangzhou 310027China

脆性金属玻璃的空化现象可追溯其本征的高原子密度涨落.有目的地调节金属玻璃内部结构以抑制其空化行为一直是被关注的问题.本文通过分子动力学模拟研究了高压热处理对脆性Fe_(80)P_(20)金属玻璃空化行为的影响.高压热处理可诱导Fe_(80)... 详细信息

脆性金属玻璃的空化现象可追溯其本征的高原子密度涨落.有目的地调节金属玻璃内部结构以抑制其空化行为一直是被关注的问题.本文通过分子动力学模拟研究了高压热处理对脆性Fe_(80)P_(20)金属玻璃空化行为的影响.高压热处理可诱导Fe_(80)P_(20)金属玻璃发生年轻化,有效抑制空化的发生.伴随压力和温度的增加,Fe_(80)P_(20)金属玻璃的空间异质性逐渐减小,同时磷原子的分布变得相对均匀.分析表明,高压热处理可诱导Fe_(80)P_(20)金属玻璃局部原子结构从“类液态”转变为“类固态”,致使空化需要更大的外加应力诱发.上述结果为理解金属玻璃的空间异质性和空化行为之间的关联规律提供了新的思路.

关键词： Metallic glass Cavitation High pressure heat treatment Molecular dynamics simulation Spatial heterogeneity

Micro- and nano-mechanics in China： A brief review of recent progress and perspectives

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Science China(Physics,mechanics & Astronomy) 2018年第7期61卷 18-31页

作者： ZhiPing xu QuanShui Zheng Applied mechanics Laboratory and center for Nano and Micro mechanics Department of Engineering Mechanics Tsinghua UniversityBeijing 100084 China

The past three decades have witnessed the explosion of nanoscience and technology, where notable research eftbrts have been made in synthesizing nanomaterials and controlling nanostructures of bulk materials. The uncovered mechanical behaviors of structures and materials with reduced sizes and dimensions pose open questions to the community of mechanicians, which expand the framework of continuum mechanics by advancing the theory, as well as modeling and experimental tools. Researchers in China have been actively involved into this exciting area, making remarkable contributions to the understanding of nanoscale mechanical processes, the development of multi-scale, multi-field modeling and experimental techniques to resolve the processing-microstructures-properties relationship of materials, and the interdisciplinary studies that broaden the subjects of mechanics. This article reviews selected progress made by this community, with the aim to clarify the key concepts, methods and applications of micro- and nano-mechanics, and to outline the perspectives in this fast-evolving field.

关键词： micro- and nano-mechanics multi-scale and multi-field methods nanotechnology nanomaterials nanostructurcs