检索结果-南通市图书馆

A new,direct approach toward modeling thermo-coupled fatigue failure behavior of metals and alloys

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Solida Sinica 2017年第1期30卷 1-9页

作者： Zhaoling Wang Hao Li zhengnan yin Heng Xiao Shanghai Institute of Applied Mathematics and Mechanics and State Key Laboratory for Advanced Special Steels Shanghai University School of Mathematics and Information Sciences Weifang University

The objective of this study is two-fold. Firstly, new finite strain elastoplasticity models are proposed from a fresh standpoint to achieve a comprehensive representation of thermomechanical behavior of metals and alloys over the whole deformation range up to failure. As contrasted with the usual elastoplasticity models, such new models of much simpler structure are totally free, in the sense that both the yield condition and the loading–unloading conditions need not be introduced as extrinsic coercive conditions but are automatically incorporated as inherent constitutive features into the models. Furthermore, the new models are shown to be thermodynamically consistent, in a further sense that both the specific entropy function and the Helmholtz free energy function may be presented in explicit forms, such that the thermodynamic restriction stipulated by Clausius–Duhem inequality for the intrinsic dissipation may be identically satisfied. Secondly, it is then demonstrated that the thermo-coupled fatigue failure behavior under combined cyclic changes of stress and temperature may be derived as direct consequences from the new models. This novel result implies that the new model can directly characterize the thermo-coupled fatigue failure behavior of metals and alloys, without involving any usual damage-like variables as well as any ad hoc additional criteria for failure. In particular, numerical examples show that, under cyclic changes of temperature, the fatigue characteristic curve of fatigue life versus temperature amplitude may be obtained for the first time from model prediction both in the absence and in the presence of stress. Results are in agreement with the salient features of metal fatigue failure.

关键词： Thermo-coupled behavior Fatigue failure Finite deformations New elastoplasticity models Direct simulation

Structure dependent elastic properties of supergraphene

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2016年第4期32卷 684-689页

作者： Juan Hou zhengnan yin yingyan Zhang Tien-Chong Chang Shanghai Institute of Applied Mathematics and Mechanics Shanghai Key Laboratory of Mechanics in Energy Engineering Shanghai University School of Computing Engineering and MathematicsWestern Sydney University State Key Laboratory of Ocean Engineering School of Naval Architecture Ocean and Civil Engineering Shanghai Jiao Tong University

Complete replacement of aromatic carbon bonds in graphene by carbyne chains gives rise to supergraphene whose mechanical properties are expected to depend on its structure. However, this dependence is to date unclear. In this paper, explicit expressions for the in-plane stiffness and Poisson＇s ratio of supergraphene are obtained using a molecular mechanics model. The theoretical results show that the in-plane stiffness of supergraphene is drastically（at least one order） smaller than that of graphene, whereas its Poisson＇s ratio is higher than 0.5. As the index number increases（i.e., the length of carbyne chains increases and the bond density decreases）, the in-plane stiffness of supergraphene decreases while the Poisson＇s ratio increases. By analyzing the relation among the layer modulus, in-plane stiffness and Poisson＇s ratio, it is revealed that the mechanism of the faster decrease in the in-plane stiffness than the bond density is due to the increase of Poisson＇s ratio. These findings are useful for future applications of supergraphene in nanomechanical systems.

关键词： Poisson stiffness chains aromatic modulus faster bonds nanotubes zigzag replacement

OBTAINING MULTI-AXIAL ELASTIC POTENTIALS FOR RUBBER-LIKE MATERIALS VIA AN EXPLICIT,EXACT APPROACH BASED ON SPLINE INTERPOLATION

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Solida Sinica 2014年第5期27卷 441-453页

作者： Hao Li Yuyu Zhang Xiaoming Wang zhengnan yin Heng Xiao Shanghai Institute of Applied Mathematics and Mechanics & Mechanics and Shanghai Key Laboratory of Mechanics in Energy Engineering Shanghai University

An explicit, exact approach is proposed to obtain multi-axial elastic potentials for isotropic rubber-like materials undergoing large incompressible deformations. By means of two direct, explicit procedures, this approach reduces the problem of determining multi-axial poten- tials to that of determining one-dimensional elastic potentials. To this end, two one-dimensional potentials for uniaxial case and simple shear case are respectively determined via spline inter- polation and, then, the two potentials are extended to generate a multi-axial elastic potential using a novel method based on certain logarithmic invariants. Eventually, each of the multi-axial potentials will exactly match the finite strain data from four benchmark tests.

关键词： elastomers elastic potentials logarithmic strain invariants benchmark tests splineinterpolation exact matching

基于单轴数据决定橡胶类材料多轴刚性化有界超弹性势

在线全文

学校读者我要写书评

暂无评论

固体力学学报 2015年第2期36卷 164-170页

作者：余利丹金天付尹征南肖衡上海大学上海市应用数学和力学研究所上海200072

指出表征橡胶类材料应变刚化效应的现有超弹性模型涉及应变能无穷发散困难,提出新方法解决该困难.基于对数应变不变量的多轴扩张和多轴匹配步骤,建议直接构造橡胶类材料大变形弹性势的显式直接方法.该方法从单轴应力-应变关系直接得到... 详细信息

指出表征橡胶类材料应变刚化效应的现有超弹性模型涉及应变能无穷发散困难,提出新方法解决该困难.基于对数应变不变量的多轴扩张和多轴匹配步骤,建议直接构造橡胶类材料大变形弹性势的显式直接方法.该方法从单轴应力-应变关系直接得到多轴弹性势,所得结果避免了现有各方法决定待定参数组的复杂数值计算,能够准确描述应变刚性化效应,且给出有界弹性应变能,从而避免了前述发散困难.数值结果表明,从单轴数据所得到的弹性势可同时很好的拟合平面应变拉伸(剪切)数据以及等双轴拉伸数据.

关键词：橡胶类材料弹性势对数应变不变量刚化应变有界应变能

在线全文

学校读者我要写书评

暂无评论

玻璃态高分子材料银纹力学研究进展

力学进展 2007年第1期37卷 48-66页

作者：王铁军尹征南王建国西安交通大学工程力学系强度与振动教育部重点实验室西安710049

银纹是玻璃态高分子材料所特有的一种现象,它既是高分子材料的塑性变形和增韧机理,又是高分子材料的损伤机理,还是连接高分子材料微观损伤与宏观破坏的桥梁．银纹的萌生、长大与断裂是高分子科学和固体力学所共同关注的难题．过去几十... 详细信息

银纹是玻璃态高分子材料所特有的一种现象,它既是高分子材料的塑性变形和增韧机理,又是高分子材料的损伤机理,还是连接高分子材料微观损伤与宏观破坏的桥梁．银纹的萌生、长大与断裂是高分子科学和固体力学所共同关注的难题．过去几十年在试验、理论和数值模诸方面也取得了显著进展,但较为系统的理论框架尚未建立,人们试图把细观力学的基本知识与高分子系统银纹化现象联系起来的设想才刚刚开始,且尚未在指导高分子合金设计方面起到关键作用．本文试图对近10多年来,高分子银纹化的研究进展予以介绍和评述．首先简要介绍银纹的基本形貌、萌生判据与生长规律,然后分别介绍银纹断裂力学、银纹损伤力学和银纹细观力学的研究进展和成果,最后概要介绍银纹分子动力学研究的最新进展．

关键词：聚合物高分子银纹断裂损伤细观力学分子动力学

用统一强度理论求厚壁圆筒和厚壁球壳的极限解

在线全文

学校读者我要写书评

暂无评论

应用力学学报 2000年第1期17卷 157-161页

作者：赵均海张永强廖红建尹征南西北建筑工程学院西安710061 西安交通大学西安710049

采用俞茂宏统一强度理论分析了厚壁圆筒和厚壁球壳的极限荷载 ,得出了统一解形式。利用此解可以合理地得出不同材料的相应解 ,它既可以适用于拉压强度相等的材料 ,也可以适用于拉压强度不相等的材料 ,并且能充分发挥材料性能 ,从而减轻... 详细信息

采用俞茂宏统一强度理论分析了厚壁圆筒和厚壁球壳的极限荷载 ,得出了统一解形式。利用此解可以合理地得出不同材料的相应解 ,它既可以适用于拉压强度相等的材料 ,也可以适用于拉压强度不相等的材料 ,并且能充分发挥材料性能 ,从而减轻结构重量。

关键词：统一强度理论厚壁圆筒厚壁球壳极限荷载

FAST SYMBOL-LEVEL SYNCHRONIZATION FOR TR-UWB SIGNALS USING DOUBLE HYBRID DS-TH SPREADING

在线全文

学校读者我要写书评

暂无评论

Journal of Electronics(China) 2008年第3期25卷 394-400页

作者： Zhang Zhuo Ji zhengnan Zhang Shijie yin Hao Institute of Communications Engineering PLA Univ. of Sci. ＆ Tech. Nanjing 210007 China Command Automation Station Joint Logistics Department of Shenyang Military Area Shenyang 110005 China Institute of China Electronic System Engineering Corporation Beijing 100039 China

A Transmitted Reference (TR) Ultra WideBand (UWB) signal with double hybrid Direct Sequence and Time Hopping (DS-TH) spreading is proposed and its symbol-level synchronization scheme is designed and analyzed. The proposed signaling format can significantly reduce the search space while reducing the spectral lines and eliminating inter-frame interference and multi-user inter- ference. Detailed analysis of the proposed scheme is carried out. Synchronization performance of the proposed signaling format in multipath channel is derived and supported by computer simulation. The search step which is closely associated with the delay of data modulated pulses is analyzed. Using the TH code, the proposed signaling format and synchronization scheme especially works well in moderate and low data rate systems.

关键词： Ultra-WideBand (UWB) Transmitted Reference (TR) Synchronization Spread spectrum CLC index TN929.5

Algebraic-Differential Attacks on a Family of Arithmetization-Oriented Symmetric Ciphers

在线全文

学校读者我要写书评

暂无评论

Journal of Systems Science & Complexity 2023年第6期36卷 2681-2702页

作者： LI zhengnan WU Baofeng LIN Dongdai Institute of Information Engineering Chinese Academy of SciencesBeijing100085China State Key Laboratory of Cryptology Beijing100878China School of Cyber Security University of Chinese Academy of SciencesBeijing100049China

Motivated by applications in advanced cryptographic protocols,research on arithmetizationoriented symmetric primitives has been rising in the field of symmetric cryptography in recent *** this paper,the authors focus on on the collision attacks for a family of arithmetization-oriented symmetric ciphers *** authors firstly enhance the algebraically controlled differential attacks proposed by introducing more ***,combining algebraic attacks and differential attacks,the authors propose algebraic-differential attacks on GMi *** attack method is shown to be effective by experiments on toy versions of GMi *** authors further introduce some tricks to reduce the complexities of algebraic-differential attacks and improve the success probability of finding collisions.

关键词： Algebraic attacks collisions differential attacks GMiMCHash Grobner basis

Palladium-Catalyzed Selective Syntheses of 2,3-Allenyl Amines via Double Functionalization Coupling of 2-Alkynyl-1,4-diol Dicarbonates

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Chemistry 2024年第19期42卷 2357-2362页

作者： zhengnan Zhou Can Li Shengming Ma State Key Laboratory of Organometallic Chemistry Shanghai Institute of Organic ChemistryChinese Academy of Sciences345 Lingling LuShanghai 200032China University of Chinese Academy of Sciences Bejjing 100049China Research Center for Molecular Recognition and Synthesis Department of ChemistryFudan University220 Handan LuShanghai 200433China

Comprehensive Summary 2,3-Allenyl amines have shown wide applicability in biomedical and synthetic *** to their enormous potential for applications,researchers have been dedicated to the development of methods for synthesizing 2,3-allenyl ***,a palladium-catalyzed three-component reaction of 2-alkynyl-1,4-diol dicarbonates,organoboronic acids,and nitrogen nucleophiles forming 2,3-allenyl amines with excellent regio-and chemo-selectivity has been *** compatibility and synthetic applications have been *** experiments supported a mechanism involving 1,2,3-triene-Pd species and methylene-π-allyl palladium species.

关键词： Pd catalysis 2,3-Allenyl amine Alk-2-yn-1,4-diol dicarbonate Organoboronic acid 1,2,3-Triene Methylene-π-allyl palladium species Regioselectivity Chemoselectivity