The strain energy criterion of mixed-mode brittle fracture

In this paper, we proposed a new cr tenon or mixea-moae brittle fracture, i.e., the strain energy criterion, which can be stated as (K_Ⅰ/K_Ⅰc)² +(K_Ⅰ/K_Ⅰc)²+(K_Ⅱ/K_Ⅱc)²=1. This criterion is shown to be in good agreement with known experimental data.In this paper, an experimental criterion:(K_Ⅰ/K_Ⅰc)^m+(K_Ⅱ/K_Ⅱc)ⁿ=1, 1≤_n^m≤2.is also proposed.     

Fixed point theorem of nonexpansive mappings in convex metric spaces

Let X be a convex metric space with the property that every decreasing sequence of nonenply dosed subsets of X with diameters tending to has menemptyintersection. This paper proved that if T is a mapping of a elosed conver nonempty subset K of X into itself satisfying the inequality:d(T_x,T_y)≤ad(x,t)+b{d(x,T_x)+d(y,T_y)}+c{d(x,T_x)+d(y,T_y)}for all x,y in K,where 0≤a<1,b≥0,c≥0,a+c≠0 and a+2b+3c≤1, then T has a unique fixed point in K.     

[0, k i]1 m -Factorizations Orthogonal to a Subgraph

Let G be a graph,k₁,…,k_m be positive integers. If the edges of graph G can be decomposed into some edge disjoint. [0,k₁]-factor. F₁,…,[0,k_m]-factor F_m, then we can say F={F₁,…,F_m, is a [0,k_i]_m¹-factorization of G. If H is a subgraph with m edges in graph G and |E(H)∩E(F_i)|=1 for all 1≤i≤m, then we can call that F is orthogonal to H. It is proved that if G is a..[0,k₁+…+k_m-m+1]-graph, H is a subgraph with m edges in G, then graph G has a. [0,k_i]₁^m-factorization orthogonal to H.     

On near-wall hot-wire measurements

A specially constructed hot-wire probe was used to obtain very near-wall velocity measurements in both a fully developed turbulent channel flow and flat plate boundary layer flow. The near-wall hot-wire probe, having been calibrated in a specially constructed laminar flow calibration rig, was used to measure the mean streamwise velocity profile, distributions of streamwise and spanwise intensities of turbulence and turbulence kinetic energy k in the viscous sublayer and beyond; these distributions compare very favorably with available DNS results obtained for channel flow. While low Reynolds number effects were clearly evident for the channel flow, these effects are much less distinct for the boundary layer flow. By assuming the dissipating range of eddy sizes to be statistically isotropic and the validity of Taylor's hypothesis, the dissipation rate ɛ _iso in the very near-wall viscous sublayer region and beyond was determined for both the channel and boundary layer flows. It was found that if the convective velocity U _c in Taylor's hypothesis was assumed to be equal to the mean velocity Uˉ at the point of measurement, the value of (ɛ⁺ _iso)₁ thus obtained agrees well with that of (ɛ ⁺)_DNS for y ⁺ ≥ 80 for channel flow; this suggests the validity of assuming U _c=Uˉ and local isotropy for large values of y ⁺. However, if U _c was assumed to be 10.6u _τ , the value of (ɛ⁺ _iso)₂ thus obtained was found to compare reasonably well with the distribution of (ɛ⁺ _iso)_DNS for y ⁺≤ 15. Received: 31 May 1999/Accepted: 20 December 1999     

基于B-样条小波的复合材料层合板灵敏度分析

基于BSWI样条小波有限元方法,将响应和响应的灵敏度系数同时看作状态变量,在Hamilton体系下推导了复合材料层合板响应和响应灵敏度系数的混合控制方程。基于该混合控制方程研究了对称铺层四边固支复合材料层合板的位移响应灵敏度系数在z方向上的分布情况,并将计算结果与有限差分法进行比较。结果表明:材料参数E₁,E₂和G₁₂对位移响应影响明显,其中以E₁对位移响应的影响最大,E₂次之。与经验法相比,半解析法计算结果相对误差小于10^-4,这说明本文的计算方法是正确的,且降低了计算成本和程序实现难度,提高了计算精度。     

压电压磁材料中正n边形孔边裂纹分析

基于电磁复合材料力学,运用Stroh型公式和复变函数方法,针对压电压磁材料中含正n边形孔边裂纹反平面问题进行了研究。利用Schwarz-Christoffel变换技术,结合Cauchy积分公式和留数定理,导出了磁电全非渗透型边界条件下任意正n边形裂纹尖端场强度因子和能量释放率的解析解。当缺失磁场时,所得解退化为已有结果,以此验证方法的有效性。通过数值算例,对比分析了n=3,n=4和n=5三种特殊情形对应的孔口边长、裂纹长度和受到的力、电和磁载荷对等效场强度因子和无量纲能量释放率的影响规律。研究结果发现,正n边形孔洞的尺寸和裂纹长度均会促进裂纹扩展,且前者的影响更显著一些;正n边形边的数量增加会阻止裂纹的扩展;在磁电全非渗透型边界条件下,机械载荷始终促进裂纹的扩展,电位移载荷可以促进或抑制裂纹的扩展,磁载荷对裂纹的扩展贡献较少。本研究结果适用于任意正n边形孔边裂纹求解问题,为压电压磁材料元器件的优化设计和断裂特性分析提供了新思路。     

改进的Park-Ang再生混凝土柱地震破坏模型的试验研究

通过对不同配比的6根再生混凝土(RAC)柱进行低周反复加载试验。由于现有普通混凝土结构地震破坏损伤模型均为基于普通混凝土结构所构建的,是否适用于RAC结构的地震损伤破坏计算仍不明确;为能够有效考虑RAC中再生骨料取代率及混杂纤维掺量等因素所造成的普通混凝土结构地震破坏损伤模型中循环荷载系数β的不确定性及其对损伤指数计算结果的影响,同时提高计算模型的预见性与可靠性,本文提出了一种适用于RAC结构的改进的双参数损伤模型。通过模型的计算结果与实际结构各震害破损度D_c的对比,确定了适用于RAC结构的双参数损伤模型中循环荷载系数β的值。     

复杂凸多面体随机紧密堆积组构性能的数值研究:形状参数的影响

颗粒材料的宏观物理力学性能依赖于颗粒堆积体系的细观组构性能,研究颗粒堆积体系的组构性能有重要意义。然而,当前对颗粒堆积体系组构性能的研究集中于球、椭球和正则多面体等规则几何体,还未有对复杂凸多面体颗粒堆积体系组构性能的系统研究。本文基于旋转椭球面黄金螺旋网格构造了一组复杂凸多面体颗粒模型(Poly_κ-ngs),然后基于松弛算法获得了Poly_κ-ngs多面体的随机紧密堆积结构,最后研究了几何形状参数对Poly_κ-ngs多面体随机紧密堆积体系组构性能的影响。结果表明,长径比κ和顶点数量n_gs均对堆积体系的组构性能有影响,κ是主要影响因素。Poly_κ-ngs多面体随机紧密堆积结构中颗粒的位置分布均匀,长径比κ越接近1,顶点数量n_gs越大时,堆积结构表现出更强的位置长程有序性;颗粒方向分布不均匀,长径比κ越远离1,不均匀程度越高;最高堆积分数随长径比κ的增大先增大后减小,在κ=1时达到峰值;配位数分布服从高斯分布,平均配位数随形状参数的变化和堆积分数不同;面-面接触数量随长径比κ的增大先增大后减小,和堆积分数变化规律一致。本研究为复杂凸多面体颗粒的随机紧密堆积提供了数值模拟方案,得出的结论对含有凸多面体颗粒材料的设计和性能优化具有参考意义。     

基于扩展有限元法的混凝土细观断裂破坏过程模拟

扩展有限元法（XFEM）是分析不连续力学问题（特别是断裂问题）的一种有效的数值方法。在常规的有限元位移模式中,基于单位分解的思想加入一个跳跃函数和渐进缝尖位移场来对不连续体附近的节点自由度进行局部加强,从而反映了位移的不连续性。介绍了扩展有限元的基本原理,给出了扩展有限元进行混凝土开裂及裂纹扩展的分析方法,最后采用扩展有限元法模拟了湿筛混凝土单轴拉伸作用下及WinklerL-型混凝土板的细观断裂破坏过程。分析了混凝土裂纹萌生、扩展的过程及破坏形态,数值结果与实验结果吻合良好。研究表明：扩展有限元法通过特定的位移模式,使裂纹两侧不连续位移场的表达独立于网格划分,能有效地模拟混凝土材料细观断裂破坏过程。     

断裂相场在循环塑性与疲劳分析中的应用

断裂是结构失效的常见方式.论文在断裂相场模型的基础上应用疲劳退化函数,将断裂相场模型拓展到非线性等向强化本构的循环塑性加载.通过自编循环塑性本构与疲劳塑性相场MATLAB程序,实现了韧性断裂相场模型在疲劳裂纹扩展分析中的应用.运用此程序,分析了疲劳退化函数中的参数和缺口尺寸对疲劳裂纹扩展的影响.首先,研究发现疲劳退化函...     

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,     

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.     

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 Sinica.     

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