求解界面裂纹应力强度因子的围线积分法

本文基于Ｂｅｔｔｉ功互等定理和双材料界面裂纹辅助场，提出了一种求解界面裂纹应力强度因子的方法，即远场围线积分法。此方法与积分径的选择无关，用有元元法计算出远离裂纹尖端的位移场和应力场，应可通过计算绕裂尖围线的积分，精确地给出界面裂纹应力强度因子ＫＩ和ＫⅡ。     

夹杂对两相材料界面裂纹的影响

根据界面上应力和位移的连续条件,得到了单向拉伸状态下,含有椭圆夹杂的无限大双材料组合板的复势解。进一步通过求解Hilbert问题,得到了含有夹杂和半无限界面裂纹的无限大板的应力场,并由此给出了裂尖的应力强度因子K。计算了夹杂的形状、夹杂的位置、夹杂的材料选取以及上、下半平面材料与夹杂材料的不同组合对裂尖应力强度的影响。计算结果表明夹杂到裂尖的距离和夹杂材料的性质对K影响较大,对于不同材料组合,该影响有较大差异。夹杂距裂尖较近时,会对K产生明显屏蔽作用,随着夹杂远离裂尖,对K的影响也逐渐减小。另外,软夹杂对K有屏蔽作用,硬夹杂对K有反屏蔽作用,而夹杂形状对K几乎没有影响。     

各向异性双材料界面裂纹扩展裂尖场

应用界面断裂力学理论和Stroh方法,研究了广义平面变形下动态裂纹沿着各向异性双材料界面扩展时的裂尖奇异应力及动态应力强度因子.双材料界面的动态裂尖区域特性主要由两个实矩阵W和D确定,且裂尖奇异应力和动态应力强度因子可以由包含这两个矩阵的柯西奇异积分方程确定,同时给出了动态应力强度因子和能量释放率的显示表达式.算例得出当裂纹以小速度扩展时,裂尖振荡因子ε与静态时几乎相同,当界面裂纹扩展速度接近瑞利波速时,ε趋于无穷大;同时得出应力强度因子及能量释放率随裂纹扩展速度的变化关系.     

有限尺寸下双材料界面附近裂纹位置对裂纹尖端的影响

随着复合材料的应用和发展,不同材料组成的界面结构越来越受到人们的重视.界面层两侧材料的性能相异会引起材料界面端奇异性,同时界面和界面附近存在裂纹会引起裂尖处的应力奇异性.因此双材料界面附近的力学分析是比较复杂的.论文建立双材料直角界面模型,在材料界面附近预设初始裂纹,计算了有限材料尺寸对界面应力场及其附近裂纹应力强度因子的影响.运用弹性力学中的Goursat公式求得直角界面端在有限尺寸下的应力场以及其应力强度系数.通过叠加原理和格林函数法进一步得到在直角界面端附近的裂纹尖端应力强度因子.计算结果表明,在适当范围内改变材料内裂纹与界面之间的距离,界面附近裂纹尖端的应力强度因子随着裂纹与界面距离的增加而减少,并且逐渐趋于稳定.分析结果可以为预测双材料结构复合材料界面失效位置提供参考.     

双压电体界面上的电偶极子和裂纹

求得了压电体双材料界面上的孤立二维电偶极子的解析解,结果表明某点电偶极子激发的应力一电位移场与该点到电偶极子的距离的平方成反比.研究了压电体双材料界面上的电偶极子对裂纹的作用,得到了问题的闭合解.在电偶极子的作用下,界面裂纹裂尖近区应力-电位移仍具有r-1/2+iεα的振荡奇异性,文中求得裂尖应力强度因子,当电偶极子距裂尖距离ρ很近时,裂尖应力强度因子与ρ-3/2-iεα成比例.     

双压电体界面上的电偶极子和裂纹5

求得了压电体双材料界面上的孤立二维电偶极子的解析解，结果表明某点电偶极子激发的应力－电位移场与该点到电偶极子的距离的平方成反比。研究了压电体双材料界面上的电偶极子对裂纹的作用，得到了问题的闭合解。在电偶极子的作用下，界面裂纹裂尖近区应力－电位移仍具有r^-1/2 iεα的振荡奇异性，文中求得裂尖应力强度因子，当电偶极子距裂尖距离ρ很近时，裂尖应力强度因子与ρ^-3/2-iεα成比例。     

I型裂纹尖端约束应力区模型及其解析解

考虑了I型裂纹尖端损伤区域内三种不同的约束应力分布形式,即右三角分布形式(情况A)、均匀分布形式(情况B)、左三角分布形式(情况C),并采用复变函数方法求得了应力强度因子与裂纹张开位移的解析解;在此基础上,通过数值计算得到了应力强度因子和裂纹张开位移随约束应力区长度、约束应力大小以及分布形式的变化规律。研究结果表明:随裂尖材料损伤程度的增加,裂尖损伤区内约束应力减小,应力强度因子和裂纹张开位移增大;约束应力的分布形式对应力强度因子和裂纹张开位移有显著影响;相对于其他区域,约束应力对裂纹尖端区域裂纹张开位移的影响较大。然而,对于裂尖损伤区域的形成与作用荷载、材料性质、构件几何尺寸之间的关系,还需要进行更为深入的研究。     

界面裂纹问题中的权函数方法

本文将Ｐａｒｉｓ等确定均匀材料中裂纹尖端应力强度因子的权函数方法推广应用到界面裂纹问题，给出了界面裂纹尖端附近或无限大体半无限界面裂纹问题的权函数的显式表达式。利用此权函数表达式可以很简便地求解界面裂纹尖端附近一些外来作用引起的应力强度因子，比如任意分布力、相变应变、位错和热等。作为一个算例，本文计算了界面一侧一个刃型位错引起的应力强度因子。     

双材料界面裂纹复应力强度因子的正则化边界元法

双材料界面裂纹渐近位移和应力场表现出剧烈的振荡特性,许多用于表征经典平方根(r1/2)和负平方根(r?1/2)渐近物理场的传统数值方法失效,给界面裂纹复应力强度因子(K1+iK2)的精确求解增加了难度.引入一种含有复振荡因子的新型"特殊裂尖单元",可精确表征裂纹尖端渐近位移和应力场的振荡特性,在避免裂尖区域高密度网格剖...     

求解界面裂纹应力强度因子的高次权函数法

从界面裂纹完备的特征展开式出发,利用伪正交特性,提出了计算界面裂纹特征展开式系数和应力强度因子的高次权函数法.文中计算的均匀材料应力强度因子,与已有结果吻合得非常好.并给出了界面裂纹的应力强度因子K1/K0和K2/K0随材料弹性模量比及裂纹长度的变化.     

The 7th International Conference on Fluid Mechanics May 24-27,2015,Qingdao,China

正http://www.icfm7.org First Announcement and Call for PapersThe objective of International Conference on Fluid Mechanics(ICFM)is to provide a forum for researchers to exchange new ideas and recent advances in the fields of theoretical,experimental,computational Fluid Mechanics as well as interdisciplinary subjects.It was successfully convened by the Chinese Society of Theoretical and Applied Mechanics(CSTAM)in Beijing(1987,     

INFORMATION FOR CONTRIBUTORS

Contributions： The Journal, Acta Mechanica Solida Sinica, is pleased to receive papers from engineers and scientists working in various aspects of solid mechanics. All contributions are subject to critical review prior to acceptance and publication.     

Preface

This special issue of PARTICUOLOGY is devoted to the first UK-China Particle Technology Forum taking place in Leeds, UK, on 1-3 April 2007. The forum was initiated by a number of UK and Chinese leading academics and organised by the University of Leeds in collaboration with Chinese Society of Particuology, Particle Technology Subject Group （PTSG） of the Institution of Chemical Engineers （IChemE）, Particle Characterisation Interest Group （PCIG） of the Royal Society of Chemistry （RSC） and International Fine Particle Research Institute （IFPRI）. The forum was supported financially by the Engineering and Physics Sciences Research Council （EPSRC） of United Kingdom,     

基于鲁棒滤波的捷联导引头视线角速度估计方法

针对捷联导引头无法直接获取视线角速度等信息的问题,研究了鲁棒滤波在大气层外飞行器捷联导引头视线角速度估计中的应用。为了建立非线性滤波估计模型,考虑目标视线角速度的慢变特性,采用一阶马尔科夫模型建立了状态方程;推导了视线角速度的解耦模型,并建立了量测方程;考虑到实际应用中存在系统噪声统计特性失准的问题,基于Huber-Based鲁棒滤波方法,设计了视线角速度滤波器,并完成了基于Huber-Based滤波方法和扩展卡尔曼滤波方法的数学仿真。仿真结果表明Huber-Based滤波方法的视线角、视线角速度及视线角加速度估计精度分别达到0.1140'、0.1423'/s、0.0203'/s2,而扩展卡尔曼滤波方法的视线角、视线角速度及视线角加速度估计精度仅分别为0.6577'、0.6415'/s、0.0979'/s~2。仿真结果证明了该方法可以有效地估计出相对视线角速度等信息,并且在非高斯噪声的条件下,依然可获得较高的估计精度,具有一定的鲁棒性。     

Guide for authors

正Each of the sections below provides essential information for authors.We recommend that you take the time to read them before submitting a contribution to Acta Mechanica Sinica.We hope our guide to authors may help you navigate to the appropriate section.How to prepare a submission This document provides an outline of the editorial process involved in publishing a scientific paper in Acta Mechanica     

Use specification of multiscale materials for life spanned over macro-, micro-, nano-, and pico-scale

Multiscale material intends to enhance the strength and life of mechanical systems by matching the transmitted spatiotemporal energy distribution to the constituents at the different scale, say—macro, micro, nano, and pico,—, depending on the needs. Lower scale entities are, particularly, critical to small size systems. Large structures are less sensitive to microscopic effects. Scale shifting laws will be developed for relating test data from nano-, micro-, and macro-specimens. The benefit of reinforcement at the lower scale constituents needs to be justified at the macroscopic scale. Filling the void and space in regions of high energy density is considered.Material inhomogeneity interacts with specimen size. Their combined effect is non-equilibrium. Energy exchange between the environment and specimen becomes increasingly more significant as the specimen size is reduced. Perturbation of the operational conditions can further aggravate the situation. Scale transitional functions and/or f_j/j+1 are introduced to quantify these characteristics. They are represented, respectively, by , and (f_mi/ma,f_na/mi,f_pi/na). The abbreviations pi, na, mi, and ma refer to pico, nano, micro and macro.Local damage is assumed to initiate at a small scale, grows to a larger scale, and terminate at an even larger scale. The mechanism of energy absorption and dissipation will be introduced to develop a consistent book keeping system. Compaction of mass density for constituents of size 10⁻¹², 10⁻⁹, 10⁻⁶, 10⁻³ m, will be considered. Energy dissipation at all scales must be accounted for. Dissipations at the smaller scale must not only be included but they must abide by the same physical and mathematical interpretation, in order to avoid inconsistencies when making connections with those at the larger scale where dissipations are eminent.Three fundamental Problems I, II, and III are stated. They correspond to the commonly used service conditions. Reference is made to a Representative Tip (RT), the location where energy absorption and dissipation takes place. The RT can be a crack tip or a particle. At the larger size scales, RT can refer to a region. Scale shifting of results from the very small to the very large is needed to identify the benefit of using multiscale materials.