关于双剪强度理论的教学探讨

在我国的材料力学教材和教学中,多数只讲授最大拉伸正应力理论、最大伸长线应变理论、最大剪应力理论、歪形能理论,以及莫尔强度理论.在讲授最大剪应力理论,即屈服准则 τ_(max)=(σ_1-σ_3)/2=c,亦即σ_1-σ_3=σ_s,时都要讲到,这个理论由于未考虑中间主应力σ_2对材料强度的影响而对材料在复杂应力状     

关于双剪强度理论的教学探讨

<正> 在我国的材料力学教材和教学中,多数只讲授最大拉伸正应力理论、最大伸长线应变理论、最大剪应力理论、歪形能理论,以及莫尔强度理论.在讲授最大剪应力理论,即屈服准则 τ_(max)=(σ_1-σ_3)/2=c,亦即σ_1-σ_3=σ_s,时都要讲到,这个理论由于未考虑中间主应力σ_2对材料强度的影响而对材料在复杂应力状     

屈服准则验证实验

<正> 在材料力学实验中,根据金属材料屈服极限和条件屈服极限的物理意义,能够很直观也比较容易地测定出金属材料的屈服极限σ_s、条件屈服应力σ_(0.2)和剪切屈服极限τ_s,根据多数零部件工作时不允许有过量塑性变形的要求,把工作应力控制在上述参数以下是很容易被人接受的.但是在复合受力状况下究竟用什么参数做为限度,尽管材料力学中第三和第四强度理     

低碳钢扭转硬化拉伸强度的实验研究

本文提出了关于提高低碳钢硬化强度指标的新方法、是将试样扭转至剪切屈服极限后,按一定梯度增加单位残余塑性扭转角θ_p,卸载后将得到的硬化试样再进行常规拉伸试验,获得扭转拉伸硬化屈服极限σ_(τs)和强度极限σ_(τb),它们超过了常规拉伸硬化的强度指标.     

弹性—幂强化材料旋转圆盘的安定分析

本文利用文[1]介绍的方法计算了弹性—幂强化材料旋转圆盘的应力σ_(ij)、残余应力σ_(ij)~r、应力强度σ_i以及残余应力强度σ_i~r。计算结果表明对于弹性—幂强化材料和幂强化材料,切向应力σ_0和应力强度σ_i的分布具有明显的差别。     

Mises屈服条件线性化的最佳逼近因子

1.引言 1864年Tresca提出:当最大剪应力达到某一极限值k时,材料便进入塑性区。在主应力空间中该条件可写成 将其在主偏应力矢量所在的π平面(σ_1+σ_2+σ_3=0)上投影,(1)式便表示正六边形。     

用全息和散斑干涉法对含穿透裂纹的有限宽薄板进行弹塑性分析

本文用激光全息和散斑干涉法,测量了含中心疲劳裂纹、双边切缝、45°斜切缝的有限宽铝合金板试件(LY12—CZ),在均匀单向拉伸载荷作用下,直至大范围屈服时,裂纹尖端附近区域的三维位移场.给出了下列结果:①裂纹尖端塑性区的尺寸、形状随载荷增加的变化情况.中心疲劳裂纹与双边切缝试件的裂纹尖端塑性区形状的比较;②裂纹尖端特征点的COD—σ/σ_s 曲线,裂纹起裂点的张开位移δ_(?)(即COD);③试件对称轴上一定标距内△—σ/σ_s 曲线,标称应变ε_0与载荷比σ/σ_s 关系,即ε_0—σ/σ_s 曲线,实验表明标称应变ε_0是衡量试件屈服情况的参数;④定量地测定了裂纹尖端附近的位移场;⑤裂纹尖端附近的应变场;⑥对失稳断裂载荷进行了塑性极限分析.并将上述结果与有关理论,实验及数值计算结果进行了比较.     

金属板材高温压缩试验

本文介绍了直接接触式加热器及金属板材800℃压缩试验技术。用自动描绘的力变形曲线测得弹性模量E和屈服强度σ_(0.2)。该试验技术所用设备简单,耗电少,操作方便,并提高了工作效率和试验精确度。     

不同屈服准则下的强化规律表示法

<正> 1.不同屈服准则下等向强化规律设在单向拉伸时的屈服应力σ随塑性应变(?)~p 变化时的强化规律表示为σ=σ_(?)+H((?)~p),H(0)=0 (1)在线性强化时可表示为     

材料持久极限曲线的逼近和疲劳与屈服强度校核的判据

本文根据材料的对称循环持久极限σ－１和静载强度极限σｂ，提出脉动循环持久极限σ０的估算公式．在此基础上，结合材料持久极限曲线，建立了塑性材料构件在应力循环特性ｒ＞０情况下对其进行疲劳或屈服强度校核的判据．     

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).