准静载作用下弹塑性微弯裂纹尖端塑性区

研究了准静载荷作用下的弹塑性弯曲延伸裂纹的塑性区.通过分析,比较精确地确定了弯曲裂纹尖端塑性区域边界上正应力与切应力的分布状态.综合考虑了准静态作用应力,塑性区域边界上正应力与切应力,利用二阶摄动方法,研究分析了弯曲裂纹尖端塑性区域的范围;预测了弹塑性裂纹的扩展路径.     

弹塑性疲劳微弯裂纹尖端塑性区问题

主要研究疲劳载荷作用下弹塑性裂纹弯曲延伸扩展问题.通过分析论证,比较精确地研究了疲劳载荷作用下弯曲延伸裂纹尖端塑性区域边界上交变应力的分布状况.综合考虑了疲劳作用应力,塑性区域交变应力,利用二阶摄动方法,研究计算了弯曲延伸裂纹尖端塑性区域的范围,并预测了疲劳载荷作用下弹塑性裂纹扩展路径.     

理想塑性介质中平面应力 静止裂纹的尖端弹塑性场

本文详细分析了理想塑性介质中平面应力I型静止裂纹的尖端弹塑性场,结果表明:裂纹尖端应力场内可以不包含应力间断线,但含有弹性区,作为这个一般解的特殊情况,当弹性区被两侧的塑性区挤压消失而尖端场成为满塑性区时,便得到Hutchinson(1968)给出的解,此外,文中还给出了另一种均匀应力区位于裂纹前方的解,这是[1]未曾得到的。     

粘弹塑性材料动态裂纹尖端场

本文采用一种弹性/粘塑性模型,对扩展裂纹尖端应力应变场进行了渐近分析。文中假定,弹性阶段的粘性效应可以略去,仅在塑性应变中粘性才起作用。对这种模型,文中导出了一种率敏感型的本构关系。并进一步导出了裂纹尖端应力应变场的动力学方程。通过量级分析,给出了尖端场的应力应变奇异性指数。并且讨论了弹性,塑性及粘性三者的匹配条件。对Ⅲ型裂纹进行了具体的分析计算。对各个不同参数的选取进行了详细的分析,讨论了解的性质随各参数的变化规律。     

幂硬化介质中平面应力动态裂纹的尖端弹塑性场

本文采用塑性动力学方程,对幂硬化介质中平面应力动态裂纹尖端场进行了渐近分析,其结果表明:在裂纹尖端附近,应力具有的奇异性,应变具有的奇异性,其中A是一个与塑性区尺寸有关的常数因子,r是离开裂纹尖端的距离,n为硬化指数,文中给出了尖端场的控制参量D,它依赖于马赫数;并且给出了各物理量的角函数。     

可压缩理想塑性体中逐步扩展裂纹顶端的弹塑性场

本文利用理想塑性固体平面应变问题的基本方程,分析了可压缩理想塑性体中逐步扩展裂纹顶端的弹塑性场,得到了关于应力的渐近场,分析了弹性卸载区的演变过程和修正的中心扇形区的发展过程,预示了出现二次塑性区的可能性,弹性可压缩性的影响明显表现在经典的中心扇形区必需加以修正,垂直于板面方向的应力偏量不再为零,而且随着新裂纹面的形成,裂纹前方的均匀应力场和紧连着的修正的中心扇形区的应力偏量将发生变化,这种变化是由于垂直于板面方向的应力偏量发生变化造成的。     

准静载作用下弹塑性微弯裂纹张开位移

综合考虑了准静态作用应力,塑性区域边界上正应力与剪应力,利用二阶摄动方法与卡氏定理计算了弯曲裂纹尖端的张开位移。研究了在不同的准静载荷条件下弹塑性弯曲延伸裂纹尖端张开位移随着弯曲裂纹形状参数的变化而变化的规律。研究表明,当初始裂纹长度与弯曲路径的形状参数为定值时,弯曲延伸裂纹尖端张开位移大小随外载荷的增大而增大,且增加的趋势非常剧烈。     

三维弹塑性受剪板表面裂纹的可靠性分析计算

本文建立了受剪应力表面裂纹塑性失稳扩展的可靠性分析模型。采用三维弹塑性模型对其综合变量Ｊ积分进行了计算，分析了在不同的无量纲裂纹尺寸和外载应力情况下，裂纹失稳扩展的失效概率分布规律，为工程检测和维修提供指导。     

裂纹起始扩展的弹塑性场

本文分析了裂纹扩展之前Ⅰ、Ⅱ混合型应力应变场演变的自相似性,并采用理想弹塑性模型给出了自相似解基本方程及边界条件.对v=1/2情况给出了尖端附近小范围应力应变的渐近解,同时讨论了满塑性区的存在条件.     

脉动拉伸载荷作用下的塑性区研究——弹塑性有限元解

本文采用加权平均弹塑性矩阵增量变刚度法,集中讨论处于脉动拉伸载荷作用下不同材料的平面应力中心裂纹板的塑性区特性,比较了有限元结果和理论、经验结果,找到了影响塑性区的主要因素,建议了准确度较好的模型和公式,考虑了裂纹尖端元素细化和分布密度的影响。     

一种基于直接计算高阶奇异积分的断裂力学双边界积分方程分析法

相对于有限元法,边界单元法在求解断裂问题上有着独特的优势,现有的边界单元法中主要有子区域法和双边界积分方程法.采用一种改进的双边界积分方程法求解二维、三维断裂问题的应力强度因子,对非裂纹边界采用传统的位移边界积分方程,只需对裂纹面中的一面采用面力边界积分方程,并以裂纹间断位移为未知量直接用于计算应力强度因子.采用一种高阶奇异积分的直接法计算面力边界积分方程中的超强奇异积分;对于裂纹尖端单元,提供了三种不同形式的间断位移插值函数,采用两点公式计算应力强度因子.给出了多个具体的算例,与现存的精确解或参考解对比,可得到高精度的计算结果.      

汶川地震诱发文家沟巨型滑坡 碎屑流基本特征及成因机制初步分析

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2008年5月12日,汶川M80地震在四川省绵竹市清平乡文家沟内诱发一巨型滑坡。通过现场调查得知,滑坡前后缘高差455m,厚度20～30m,滑面为基岩层面,初始方量2750×107m3。滑体在运动中转化为碎屑流。滑坡-碎屑流总的水平运动距离为4022m,垂直运动距离为1443m,遗留的堆积物体积达5×107m3。滑坡距映秀—北川断裂仅36km,位于其下盘,地震烈度达XI度。滑坡导致文家沟中48人遇害,并形成一条完整的地震次生地质灾害链。初步分析表明滑坡启动速度快,滑坡向碎屑流转化过程明显、地点明确。碎屑流运动过程复杂,伴有强烈的“气垫效应”和“前缘气浪冲击效应”。作者认为,文家沟滑坡的高启动速度是长持时强烈地震动作用的结果,与山体的猛烈碰撞是导致滑体解体并转化为碎屑流的原因。     

Preface: Orbits around asteroid

One of the core issues in modern celestial mechanics is the orbital dynamics in the near-regime gravitational field of as- teroids, which provides deep insights into the mathematical nature of a class of nonlinear systems, and plays as a critical basis for in situ explorations of different science goals. Lots of efforts have been made to reveal the characteristics of orbital motion in the vicinity of asteroids, and to improve the skills of asteroid research in methodology.     

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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Effet de l'anisotropie élastique cristalline sur la distribution des facteurs de Schmid à la surface des polycristauxInfluence of crystalline elasticity anisotropy on Schmid factor distribution at the free surface of polycrystals

Experimental studies of the plasticity mechanisms of polycrystals are usually based on the Schmid factor distribution supposing crystalline elasticity isotropy. A numerical evaluation of the effect of crystalline elasticity anisotropy on the apparent Schmid factor distribution at the free surface of polycrystals is presented. Cubic elasticity is considered. Order II stresses (averaged on all grains with the same crystallographic orientation) as well as variations between averages computed on grains with the same crystallographic orientation but with different neighbour grains are computed. The Finite Element Method is used. Commonly studied metals presenting an increasing anisotropy degree are considered (aluminium, nickel, austenite, copper). Concerning order II stresses in strongly anisotropic metals, the apparent Schmid factor distribution is drifted towards small Schmid factor values (the maximum Schmid factor is equal to 0.43 instead of 0.5) and the slip activation order between characteristic orientations of the crystallographic standard triangle is modified. The computed square deviations of the stresses averaged on grains with the same crystallographic orientation but with different neighbour grains are a bit higher than the second order ones (inter-orientation scatter). Our numerical evaluations agree quantitatively with several observations and measures of the literature concerning stress and strain distribution in copper and austenite polycrystals submitted to low amplitude loadings. Hopefully, the given apparent Schmid factor distributions could help to better understand the observations of the plasticity mechanisms taking place at the free surface of polycrystals. To cite this article: M. Sauzay, C. R. Mecanique 334 (2006).     

Nonlinear behavior of matrix-inclusion composites under high confining pressure: application to concrete and mortar

This paper is devoted to a micromechanics-based simulation of the response of concrete to hydrostatic and oedometric compressions. Concrete is described as a composite made up of a cement matrix in which rigid inclusions are embedded. The focus is put on the role of the interface between matrix and inclusion which represent the interfacial transition zone (ITZ). A plastic behavior is considered for both the matrix and the interfaces. The effective response of the composite is derived from the modified secant method adapted to the situation of imperfect interfaces. To cite this article: T.H. Le et al., C. R. Mecanique 336 (2008).