Representation of crack-tip plasticity in pressure sensitive geomaterials

This paper presents a model based on dislocation theory for representation of crack tip plasticity in a pressure sensitive material. The basic equations are derived from a simple model of the crack tip plasticity which represents the plasticity by superdislocations placed at the effective centres of the complete slip process distributed around the crack tip. The positions and strengths of the superdislocations are determined by imposing the following conditions:(i) the total stress-intensity factor at the crack tip is zero(ii) the total stress minus the self stress of the superdislocation acting at the superdislocation position is just equal to the friction stress due to the Mohr-Coulomb yield criterion and(iii) the total crack opening displacement produced by the model is maximized.Condition (iii) enables the angle of the slip band on which the superdislocation lies to be determined. The results are presented in a dimensionless form allowing the discussion of particular cases and the recognition of the dominant parameters. A series of parametric studies are carried out to demonstrate that the model can capture the essentials of the crack tip plasticity.     

可溶性碳纳米管的大规模制备

提出了一种大规模制备可溶性碳纳米管的有效而简便的方法.对制备的可溶性碳纳米管进行了表征,并测定了可溶性碳纳米管在多种有机溶剂中的溶解度以及碳纳米管在可溶性碳纳米管中的含量.     

受扭圆柱壳的大范围皱曲

本文给出受扭圆柱壳大范围皱曲的一种变形模式,从而求出不同转角时壳体的轴向缩短量以及壳体所吸收的塑性变形能的变化,计算结果和实验相符较好。     

大尺寸测量系统运动目标测量能力校准现状

分析包括全站仪、激光跟踪仪、动态工业摄影测量系统、i GPS/wMPS、激光跟踪干涉仪在内的,目前工业测量中使用较多且具有运动目标测量能力的大尺寸测量系统的基本原理,总结国内外主要相关标准和规范对这些系统动态性能的校准和评定方法,给出部分系统的校准试验结果。展望了动态测量系统校准方法的发展方向,为大尺寸测量系统的使用和校准提供参考。     

高精度大型工件内径自动测量系统

分析了目前国内外大内径的测量方法，介绍了作者研制的高精度机械测杆式大型工件内径自动测量系统，并进行了误差分析。     

大尺度空间中烟气运动工程分析的多单元区域模拟方法

在大尺度空间中，仍然将整个空间划分上部热烟气层和下部的冷空气层直接进行区域模拟是不合适的。提出了一种将大尺度空间划分若干常规子单元，再在各个子单元中采用上下层区域模拟的方法，并以CFAST4.02为工具，对两种典型的大尺度空间的烟气运动过程进行分析和比较。结果表明，在大尺度空间中，这种多单元区域模拟的方法相比于传统的区域模拟方法具有较好的适用性。     

一种基于模式搜索的大尺寸测量移站坐标转换方法

针对空间大尺寸测量的移站坐标转换，提出了最小二乘坐标转换数学模型和基于模式搜索的参数求解方法，实验证明该方法具有理论正确性和实际可行性。     

大尺寸密闭空间内甲烷—空气混合过程的数值模拟

根据10 m3多功能步入式爆炸罐的结构特点,依据进气—混气一体化的设计理念,建立了适用于10 m3爆炸罐的轴对称直管式进气—混气系统,并利用计算流体力学软件FLUENT,对进气—混气系统的具体设计参数进行了优化。通过模拟得到了直管上不同开孔孔径、开孔间距条件下小孔体积流量率的变化规律,发现减小整体开孔孔径、减小开孔间距、调整个别小孔大小能够提高小孔体积流量率的一致性,达到气体快速均匀混合的效果。     

云南大型超大型矿床与壳幔界面相关性研究及其预测

简述了壳幔界面的成矿理论及云南幔坳特征,归纳出4条规律:金属矿床对称地展布在幔坳的两侧斜坡上;云南迄今57个大型矿床的幔距≤20km,其中94·7%≤16km,幔角≤1°;幔角≤0·6°的波台更利于形成超大型矿床;大型矿床与超大型矿床间的关系服从0·618黄金律。预测云南省境内共有大型矿床450个以上,超大型矿床79个以上。     

大空间坐标测量网络的现场实时标定方法

大空间坐标测量网络主要由若干测量基站组成,为在测量现场完成网络的构建,并在测量过程中实时重新标定测量基站的空间坐标,通过对网络的测量原理及测量基站的结构进行分析,提出了模拟基站的标定模型。该模型将球形标靶作为模拟基站,并将模拟基站布置在特定位置上,可解决共面布局下测量网络的标定问题。为获取标定模型所需的距离信息,提出了主动扫描和寻心扫描两种瞄准测距方法。仿真标定实验结果表明,当测距精度为0.5 mm时,测量基站的坐标标定误差均值为2.1 mm。瞄准实验结果表明,两种瞄准方法所得测距值标准差分别为0.16 mm和0.34 mm,与测距精度相当。     

高端装备大型零部件几何尺寸测量技术现状及趋势

高端装备的大型零部件几何尺寸测量与控制是保证产品交付质量的基础,高端装备性能及产量的提升对几何尺寸测量提出了更高的精度与效率要求.本文结合大型零部件几何参数测量需求,介绍了大尺寸坐标测量、扫描测量、姿态测量、协同测量、组网测量、动态测量六种大尺寸测量技术的工作原理、典型仪器以及应用特点,分析了固定式测量系统和柔性测量系...     

Influence of residual thermal stresses on fatigue crack growth life of discontinuous reinforcements in metal matrix composites

The fatigue life prediction model based on crack propagation from micro-structural features is derived and presented for planar and randomly oriented Discontinuous Reinforced Metal Matrix Composites (DRMMCs). The model contains the influence of micro-structural properties such as aspect ratio, volume fraction of particle/fibre and constraint between particle and the matrix. The effect of residual thermal stresses generated within the matrix during development of composite is considered. The particle/fibre plays a dominant role in the development of the cyclic plastic zone size ahead of the crack tip; moreover, it enhances the cyclic plastic deformation characteristics of DRMMC. The theoretical model-based evaluations for low cycle fatigue in DRMMCs are within the proximity of the experimental results.     

Large strain finite element analysis of a local second gradient model: application to localization

The original article to which this Erratum refers was published in the International Journal for Numerical Methods in Engineering 2002; 54 :365–398.     

Scale effects on the in-situ tensile strength and fracture of ice Part I: Large grained freshwater ice at Spray Lakes Reservoir, Alberta

At lab-scale, issues such as inhomogeneity and polycrystallinity are especially important to the fracture of S1 freshwater ice. S1 freshwater ice is typically composed of large grains with predominantly vertical c-axes. Because of the very large grain sizes that one can encounter in S1 macrocrystalline ice sheets, it is essential that the effects of sample size on the fracture behavior be determined. In other words, are small scale (lab-scale) results applicable at larger scales (at the scale of ice-structure interactions, for instance)? To answer this question, a set of lab- to structural-scale (0.34>L>28.64m) fracture tests were conducted on S1 freshwater lake ice at Spray Lakes, Alberta, using the base-edge-notched reverse-tapered plate geometry and covering a size range of 1:81. A Ba?ant-type size effect analysis of the measured fracture strengths (which do reveal a significant dependence on scale) is unexpectedly clouded by the fact that the data collected violates the associated scatter requirements, even though the size range tested is large. Moreover, via Hillerborg's fictitious crack model, large fracture energies were back-calculated (of order 20 J/m2), but for miniscule process zone sizes; in addition, not all of the measured deformations for each test could be matched simultaneously. Apparently, these very warm S1 macrocrystalline lake ice experiments were dominated by nonlocal deformation and energy release rate mechanisms, in all likelihood brought about by grain boundary sliding. The reduced effectiveness of both the Ba?ant-type size effect analysis and Hillerborg's fictitious crack model is due mainly to the lack of crack growth stability achieved in the experiments. These unstable fractures truncated the fracture process. Given the irregular and large grain structure, the very warm ice temperatures, and the diffuse grain boundary surface energy, there is a marked dependence on specimen size to grain size ratio and distinctly non-unique pre-failure process zones occurred. Micromechanical simulations are required to resolve these coupled issues.     

Effects of Shear‐Transverse Coupling and Plasticity in the Formulation of an Elementary Ply Composites Damage Model,Part I: Model Formulation and Validation

Abstract: Continuum damage mechanics (CDM) models have been employed successfully in the literature to predict the response of laminated composite materials. Some sophisticated models can include the effects of non‐linear shear and transverse damage progression, plasticity and shear‐transverse damage coupling. However, these models require non‐standard test data for calibration that may not always be available to a modeller. In this two‐part study, we examine the effect of neglecting plasticity parameters, and also the effect of neglecting both plasticity and shear‐transverse coupling parameters in simplified CDM models for predicting monotonic tensile strength. In part I, we develop simplified versions of the CDM model and test their ability to accurately predict the failure response of angle‐ply laminates. In part II, we provide details of the experimental test series carried out to determine the input parameters for the models. It was found that neglecting plasticity requires some approximations in the damage development laws, but the resulting model can predict well the response of the angle‐ply laminates tested under monotonic loading to failure. Neglecting shear‐transverse coupling is acceptable for the some materials.     

中国近海油气勘探进展

近年来,中国近海的油气勘探坚持以寻找大中型油气田为指导思想,以区域研究为基础,以科学合理部署为保证,针对中国近海独特的油气地质特征,通过创新认识和技术进步,坚持走高效勘探之路,取得了丰硕成果,新发现储量屡创历史新高,步入了历史上最好时期。然而,随着勘探程度的提高和勘探领域的拓展,中国近海油气勘探也面临越来越多的挑战。