单试样三曲线法测定J积分阻力曲线及条件起裂值

用单试样三曲线法测定了16MnR 钢和某一焊缝金属的 J 积分阻力曲线及其条件起裂值,与标准的多试样测定结果基本吻合.实验表明,单试样三曲线的关联分析反映了带裂纹的三点弯曲试样的宏观断裂物理过程,裂纹的延性扩展符合幂函数规律.     

单试样法测金属材料J_R曲线及其条件起裂值

在单试样卸载柔度法及三曲线法基础上 ,提出了一种更简便的测定金属材料 JR曲线及其条件起裂值的单试样三点柔度法 ,并用该方法测定了 1 Cr1 / 2 Mo钢、1 6Mn R钢和 WCF62钢的 JR曲线及其条件起裂值 ,与标准的多试样法相比 ,误差均在工程许可范围内     

单试样法测金属材料JR曲线及其条件起裂值

在单试样卸载柔度法及三曲线法基础上,提出了一种更简便的测定金属材料JR曲线及其条件起裂值的单试样三点柔度法,并用该方法测定了1Cr1/2Mo钢、16MnR钢和WCF62钢的JR曲线及其条件起裂值,与标准的多试样法相比,误差均在工程许可范围内。     

用双悬臂梁（DCB）试样测定JR曲线的实验方法

本文首先建立了双悬臂梁(DCB)试样的 J 积分和加载点位移Δ的半解析解,然后提出了一种利用 CDB 试样测定材料.J_R 阻力曲线的单试样方法,并对40Cr 钢材进行了实际测试.结果表明,该方法不仅简单易行、结果可靠,而且获得的材料 J_R 曲线的Δα范围较宽.     

韧性材料J_R阻力曲线受试样尺寸因素影响的实验研究

本文应用不同尺寸的三点弯曲试样和带边侧槽试样,用实验方法研究了启裂J积分(J_(1C))和J_R阻力曲线的斜率(dJ/da)受试样尺寸的影响。结果表明,在满足GB2038-80所规定的试样尺寸要求的条件下,J_(1C)值受试样尺寸影响不大,但DJ/da值受试样尺寸影响较大。因此,在应用以J_R曲线理论为基础的裂纹扩展稳定性评定方法时,如撕裂模量理论及EPRI方法,要应用较大尺寸试样或带侧槽试样来测定J_R阻力曲线。     

一种基于DIC测量单边缺口拉伸试件CTOD阻力曲线的简便方法

针对测量单边缺口拉伸(SENT)试样的裂纹尖端张口位移(CTOD)阻力曲线时,延性裂纹扩展量的计算过于复杂的问题,提出了一种由数字图像相关技术(DIC)计算的变形场来确定裂纹尖端位置,并快速推算延性裂纹扩展量的方法。该方法首先在缺口和裂纹上下方的弹性区域设置两条平行横线;然后通过两条横线间的位移差构建曲线,曲线变化幅度的临界点即为裂纹端部的位置;根据临界点位置计算裂纹扩展量,最后测量CTOD并构建阻力曲线。将本文方法与另一种通过DIC测量SENT试样CTOD阻力曲线的方法进行对比,结果表明本文方法经过简便的计算后拟合的阻力曲线效果更好。     

试样尺寸对有限裂纹扩展的J_R阻力曲线的影响

作者将两种强度级别的18CrNiW 钢:σ_(0.2)=60.4kgf/mm~2(L 钢)和σ_(0.2)=83.6kgf/mm~2(H 钢),制成厚度从10mm 到95mm,共11种尺寸的三点弯曲试样,采用多试样法,在有限裂纹扩展(△α≤2.5%B 及≤5%b)条件下,测定了材料的J 积分阻力曲线.其中H 钢50×100mm 的大试样已接近K_(1c)的尺寸要求,所测得的K_(1c)约为470kgf·mm~(-3/2).试验表明,当试样尺寸满足了J 判据有效性条件时,对试验材料B,b≥50(J_(0.05)/σ_(0.2)),J_R 阻力曲线对试样尺寸不敏感.因此,J_R 阻力曲线可以用来表征材料裂纹稳定扩展阻力特性.本试验测得L 钢的J_(0.05)=9.4kgf/mm,dJ/dα=27kgf/mm~2;H 钢的J_(0.05)=7.3kgf/mm,dJ/dα=16kgf/mm~2.对于H 钢裂纹扩展量0.2mm 的J_R 值,即J_(0.2)(=9.7kgf/mm,由此换算的K_R 值=473kgf·mm~(-3/2))与大试样的K_(1c)值有很好的对应关系.     

主导曲线法测定J阻力曲线的研究

本文利用主导曲线法测定了国产核容器用钢材料Ａ５０８－３的Ｊ阻力曲线，并将实验结果与卸载柔度法作了对比，进而说明这种新方法有其广阔的应用前景；同时，本实验引入了计算机数据实时采集及自动处理系统．这些系统的引入大大提高了实验精度和效率．     

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介绍降载柔度单试件法测量柱试件ＣＯＤ阻力曲线的基本原理和运用微机采集与处理数据的方法,测定圆试件ＨＱ６０钢的ＣＯＤ阻力曲线,试验结果表明用降载柔度法测量圆柱试件ＣＯＤ阻力曲线有高很精度。     

表面疲劳裂纹扩展性能曲线测试的小样本方法

提出了一种测试表面疲劳裂纹扩展性能曲线的小样本方法,该方法可以综合利用以往的经验数据和当前试验数据劳裂纹扩展性能曲线。与传统的只能利用当前试验数据确定表面疲劳裂纹扩展性能曲线相比,其可利用的信息量有了大幅度增加,所以,在精神相同的民政部下,可以节省大量试件;而且在试样数一定的情况下又可大大提高预测精度。文中还给出了一个试验对比实例。     

Preface: Current research progress on mechanics of high speed rail

The construction and operation of high-speed rail（HSR）grid within the past two decades in China,in terms of the scale,may be possibly comparable to any national-wide construction in the history of China,even the Great Wall.By counting railways with commercial train service at the speed of200 km/h,China has the world’s longest HSR network with over 19 369.8 km of track in service today and this number     

ACTA MECHANICA SINICA 2014 ANNUAL SUBJECT INDEX

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人造地震动合成中的位移误差分析

三角函数级数法是合成人工地震动常用算法之一,但是通过对加速度积分求取位移时,却存在与零线漂移相类似的位移漂移现象。     

Rainwater rivulets on a cable subject to windFilets d'eau de pluie sur un câble soumis au vent

Rainwater rivulets appear on inclined cables of cable-stayed bridges when wind and rain occur simultaneously. In a restricted range of parameters this is known to cause vibrations of high amplitudes on the cable. The mechanism underlying this effect is still under debate but the role of rainwater rivulets is certain. We use a standard lubrication model to analyse the dynamics of a water film on a cylinder under the effect of gravity and wind load. A simple criterion is then proposed for the appearance and position of rivulets, where the Froude number is the control parameter. Experiments with several geometries of cylinder covered with water in a wind tunnel show the evolution of the rivulets with the Froude number. Comparison of the prediction by the model with these experimental data shows that the main mechanism of rivulet formation and positioning is captured. To cite this article: C. Lemaitre et al., C. R. Mecanique 334 (2006).     

Hermitian space-time finite elements for estuarine mass transport

Space-time finite element solutions of the convection–dispersion equation using higher-order nodal continuity and Hermitian polynomial shape functions are described. Five separate elements ranging from a complete linear element with C^0,0 nodal continuity to a complete first-order Hermitian element with C^1,1 nodal continuity are subjected to detailed analysis. Wave deformation analyses identify the source of leading or trailing edge oscillations, trailing edge oscillations being the major source of difficulty. These observations are confirmed by numerical experiments which further demonstrate the potential of higher-order nodal continuity. The performance of the complete first-order Hermitian element is quite satisfactory and measurably superior to the linear element.     

Cristallisation par onde acoustique : le cas de l'héliumCrystallization by acoustic waves: the case of helium

We establish a theoretical model to explain the nucleation of a crystal of helium by an acoustic over-pressure. We explain the interfacial laws for this ultra-fast cristallization, close to the sound speed. Assuming spherical symmetry and taking into account the experimental data, we recover the dynamics of the growth and melting during an over-pressure impulse. To cite this article: M. Ben Amar et al., C. R. Mecanique 331 (2003).     

Structure initiale et propriétés de liquéfaction statique d'un sableInitial structure and static liquefaction properties of sand.

Based on the use of two different preparation procedures for reconstituting triaxial samples of sand, i.e. wet tamping and dry pluviation, significant differences in associated mechanical behaviour are observed on a reference sand with respect to the phenomenon of ‘static’ liquefaction. Wet tamping favours the initiation of liquefaction instability, whereas dry pluviation favours a more stable behaviour, less susceptible to liquefaction. Microscopic observation of corresponding sand specimens allows us to identify two well differentiated structures, i.e., for wet tamping, an irregular structure with predominance of aggregates (aggregated grains) and macropores, very contractant and unstable and, for dry pluviation, a more regular structure, without macropores, more dilatant and more stable. These observations show the importance of further characterization, based on the introduction of appropriate parameters, of the initial structure of sandy materials, strongly dependant upon their mode of formation (natural or artificial). To cite this article: N. Benahmed et al., C. R. Mecanique 332 (2004).     

Sources of Complexity in Human Systems

Complex is a special attribute we can give to many kinds of systems. Although it is used often as a synonym of difficult, it has a specific epistemological meaning, which is going to be shared by the incoming science of complexity. Difficult is an object which, by means of an adequate computational power, can be deterministically or stochastically predictable. On the contrary complex is an object which can not be predictable because of logical impossibility or because its predictability would require a computational power far beyond any physical feasibility, now and forever. For complexity refers to some observing system, it is always subjective, and thus it is defined as observed irreducible complexity. Human systems are affected by several sources of complexity, belonging to three classes, in order of descending restrictivity. Systems belonging to the first class are not predictable at all, those belonging to the second class are predictable only through an infinite computational capacity, and those belonging to the third class are predictable only through a trans-computational capacity. The first class has two sources of complexity: logical complexity, directly deriving from self-reference and Gödel's incompleteness theorems, and relational complexity, resulting in a sort of indeterminacy principle occurring in social systems. The second class has three sources of complexity: gnosiological complexity, which consists of the variety of possible perceptions; semiotic complexity, which represents the infinite possible interpretations of signs and facts; and chaotic complexity, which characterizes phenomena of nonlinear dynamic systems. The third class coincides with computational complexity, which basically coincides with the mathematical concept of intractability. Artificial, natural, biological and human systems are characterized by the influence of different sources of complexity, and the latter appear to be the most complex.