压力容器高应变区应变疲劳裂纹扩展试验研究

针对压力容器几何结构不连续高应变区断裂和疲劳破坏特点,本文通过对应变循环条件下疲劳裂纹扩展影响因素和控制参量的理论分析,提出将△J作为应变循环条件下疲劳裂纹扩展速率的控制参量,并在EPRI弹塑性断裂分析工程方法基础上,提出了△J的工程计算方法,并通过模拟应变疲劳裂纹扩展的SCT试样试验,验证了△J工程计算方法的可靠性,根据SCT试样应变疲劳裂纹扩展试验研究结果,在考虑了压力容器高应变区几何形状和材质变化对应变疲劳裂纹扩展参量影响后,提出了一种压力容器高应变区应变疲劳裂纹扩展速率工程估算方法。     

镍基单晶合金非对称循环载荷低周疲劳实验研究与寿命预测

对三种不同晶体取向的DD3单晶合金试样在680℃温度下进行非对称循低周疲劳试验,表明晶体取向对疲劳寿命有显著影响.用取向函数修正总应变范围可在很大程度上消除晶体取向对疲劳寿命的影响,引入参量k表示非对称循环载荷对疲劳寿命的影响,它与循环寿命之间呈幂函数关系.根据影响单晶合金低周疲劳寿命的主要因素,提出由总应变范围、取向函数和参量k构成循环塑性应变能的计算方法。用塑性应变能作为损伤参量导出单晶合金低周疲劳寿命预测模型,利用DD3单晶合金低周疲劳试验数据进行验证,光滑试样和缺口试样试验数据分别落在2.6倍和2倍的偏差分布带内.     

谱载荷下疲劳裂纹扩展随机规律的实验研究

简要介绍了谱载荷下疲劳裂纹扩展试验的理论基础、方法和过程。讨论了各种数据处理方法对参数估计的影响,研究了疲劳裂纹扩展的随机规律。由试验得到的疲劳裂纹扩展试验数据估计了裂纹扩展方程的参数,计算出结构可靠度曲线,通过对试验结果的分析难证了以下结论：以时间为参量的裂纹扩展随机过程模型和以裂纹长度为参量的模型在一定条件下是统一的;数据处理方法的选择与可靠性分析的结果有密切的联系;裂纹扩展寿命受裂纹扩展队机     

航空发动机涡轮盘裂纹萌生寿命的估算方法

针对航空发动机涡轮盘裂纹萌生寿命的估算问题，给出一个全新的损伤参量。该损伤参量结合了分析多轴疲劳的临界面方法，“应力功”的概念和疲劳破坏的微观机制。依据该损伤参量，利用有限元程序和自编程序计算得出损伤参量和疲劳循环次数的关系，建立以这一损伤参量为基础的疲劳损伤累积模型，进而估算涡轮盘裂纹萌生寿命。     

7075铝合金扭转微动疲劳行为研究

在基于多轴疲劳试验机上自主设计的扭转微动疲劳装置上,对7075铝合金材料进行了扭转微动疲劳试验,讨论了相同法向载荷下不同扭转切应力对扭转微动疲劳寿命的影响,建立了7075铝合金扭转微动疲劳S-N曲线,并采用SEM,EDS,EPMA等分析方法对扭转微动疲劳的损伤区域进行了分析,建立了扭转微动疲劳混合区接触表面损伤和裂纹萌生及扩展的物理模型,揭示了7075铝合金扭转微动疲劳的损伤机理.试验结果表明:微动作用导致疲劳寿命大大降低;扭转微动疲劳S-N曲线呈"ε"型曲线特征;损伤区靠加载端位置氧化严重,氧化程度随着循环次数增加而增加;微动疲劳的裂纹萌生于次表面,接触区中心两侧主裂纹扩展交叉后垂直于接触表面扩展至试样断裂.     

阵风谱载下疲劳寿命可靠性预测

基于维概率ＭＩＮＥＲ准则,建立了在阵风谱载下对结构构件疲劳寿命进行可靠性预测的方法。根据一组ＬＹ１２－ＣＺ铝合金中心孔试件的疲劳试验数据对上述方法进行了较为成功的验证,验证结果表明本方法的预测值与试验值吻合良好,具有较好的工程实用价值     

一种FRP累积损伤模型及其在结构疲劳寿命估算中的应用

推荐了一种应变损伤累积模型，能够考虑单向板面内多轴应力和平均应力的影响。只需要单向板在确定应力比下的若干典型疲劳试验结果，就可以预测相同材料体系多向层压结构在不同应力比的循环载荷下的疲劳寿命，有助于降低试验成本和工作量。研究了适用于多向层压结构剩余强度估算和疲劳寿命预测的步骤和程序。针对碳纤维／树脂基T300／QY8911复合材料，试验测定了三组典型单轴循环应力（[0]16拉－拉、[90]16拉－拉和[0/90]4S剪－剪）下的S－N曲线。以此为输入，预测四种多向铺层板在各种拉－拉循环应力下的疲劳寿命，寿命预测结果和相应的试验结果吻合良好。采用了保持计算和试验的载荷／强度比相对等值的方法来近似抵消层合效应对疲劳寿命的影响。强调了进一步发展能够定量估计层间应力影响与分层扩展过程的疲劳损伤模型的重要性。     

疲劳对比试验的可靠寿命假设检验

本文直接将疲劳对比试验的可靠寿命（安全寿命）进行对比试验，提出了可靠寿命对比的假设检验方法，通过此方法对试验结果进行判断，可以检验子样是否来自可靠寿命相同的母体，了解工艺方法或设计方案的改变对疲劳性能的影响，它为疲劳对比试验假设检验提供了一新途径。     

不均匀裂纹体疲劳裂纹扩展的实验研究和分析

本文提出了裂纹在硬区的软对硬不均匀裂纹体的力学分析模型.疲劳实验研究表明,这种不均匀性影响疲劳裂纹扩展速率.文中的疲劳载荷下不均匀裂纹体的边界元数值计算结果表明,随着疲劳裂纹的扩展,在相同扩展步下,裂纹距软硬区界面越近,裂纹张开位移的幅值△COD 越小,J 积分幅值△J 亦越小.不均匀性对疲劳裂纹扩展速率的影响,主要通过影响△J 来实现.裂纹与软硬区界面的距离越近,疲劳裂纹扩展速率越小.     

铝合金切口件在四组变幅载荷下3.5%NaCl溶液中腐蚀疲劳裂纹起始寿命 …

试验研究了铝合金切口件在４组变幅块谱下，３．５％ＮａＣｌ溶液中腐蚀疲劳纹裂起始寿命，结果表明，变幅载荷谱中的大超载会显著延长腐蚀疲劳裂纹起始寿命，并且加载顺序具有明显的影响，根据反映大小载荷交互作用的超载腐蚀疲劳裂纹起始寿命曲线和Ｍｉｎｅｒ累积损伤定理，建立变幅载荷下切口件腐蚀疲劳裂纹起始寿命估算模型，应用该模型估算的结果与试验结果相吻合。     

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


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.     

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).     

Dynamics and Breakup of Viscoelastic Liquids (A Review)

The phenomena of hydrodynamic breakup of liquid jets, drops, films, bridges, and filaments are reviewed for liquids with viscoelastic properties. The reasons for breakup are capillary instabilities, collisions with rigid obstacles, and other forms of dynamic action. The relationship between the properties of the liquids and the features of the breakup process is discussed.     

Flow stability analysis and excitation using pulsating jets

Classical flow stability applied to transition from laminar to turbulent flow may also describe the behavior of vorticity fluctuations created by a pulsating jet placed along a solid boundary. A numerical laminar flow experiment involving a pulsating jet placed along the surface of a duct with flow separation downstream, resulted in eliminating most part of the separated flow region. Applying the same approach to a turbulent flow, it was possible to develop a turbulent stability flow formulation and apply successfully turbulent pulsating jet flow separation control. To cite this article: D. Skamnakis, K. Papailiou, C. R. Mecanique 333 (2005).