柱状装药爆炸条件下厚壁圆筒爆室内 流场及结构动力响应分析

借助非线性动力有限元程序ANSYS/LS-DYNA,采用基于罚函数的流固耦合算法,对厚壁圆筒爆 室在柱状装药爆炸作用下的动态响应过程进行了数值模拟研究。分析了厚壁圆筒爆室内柱状装药爆炸非定 常流场的演化过程以及筒体的动力响应特征。给出了爆炸流场的压力云图、筒壁受到的爆炸压力峰值及冲量 的分布规律、筒体的等效应力云图以及等效应力的分布规律等。流场压力及筒体应变的计算结果与实测结果 吻合较好,并将动力响应的有限元计算结果与理论解进行了比较,证明轴对称平面应变假设下的理论解可以 给出问题的保守估算。分析表明,该厚壁圆筒爆室在柱状装药爆炸作用下在弹性范围内工作,爆室的强度设 计是安全的。     

复合材料厚壁圆筒的疲劳损伤研究

基于能量耗散法，推导出了复合材料厚壁圆筒的疲劳损伤和疲劳寿命函数；在此基础上，采用有限元软件 ABAQUS 建立复合材料圆筒模型，进行了模拟周期内压载荷作用下的疲劳仿真计算，得到了随着循环数的增加，疲劳损伤变量不断增大和材料性能不断退化的损伤规律。以同样的方法和载荷边界条件计算了全金属圆筒疲劳损伤的起始和演化。对比结果表明：相同循环次数作用下，后者的裂纹扩展长度和张开位移更大；随着循环次数的增加，后者的疲劳破坏比前者更剧烈，更难预测。     

一种散体材料SHPB被动围压试验体应力修正方法

本文利用有限元仿真给出了一种修正方法，并用数值仿真和试验验证了该方法的可靠性。研究表明:散体材料SHPB被动围压试验中，试样厚度远小于厚壁圆筒长度时，端部效应会导致厚壁圆筒不均匀凸出变形，计算材料的体应力-应变关系不能将厚壁圆筒应力状态简化为平面应力问题；厚壁圆筒处于弹性状态下，通过厚壁圆筒理论计算出的径向力与真实径向力存在一定比例关系，在一定范围内，折算系数与试样实时厚度呈二次函数关系。     

脉冲载荷作用下钢梁动力响应及反常行为的应变率效应

为了讨论率敏感材料软钢钢梁受矩形脉冲载荷作用下的动力响应问题,通过直接离散有限变形弹 塑性连续体最小加速度原理中的Lee泛函得到基本控制方程,并将包含应变率的Cowper-Symonds方程嵌入 应力-应变关系方程,使该计算模型计及材料的应变率效应,因而能够准确描述钢梁受爆炸和冲击载荷作用下 的动力响应问题。该计算模型的有效性通过与通用有限元程序ABAQUS比较而得到了验证,并进一步与已 有的刚塑性解做了对比。利用该计算模型进行数值计算,分析了均布和集中脉冲载荷作用下钢梁动力响应的 应变率效应,结果发现对于钢梁存在新的异常行为响应模式,应变率导致异常区域偏移和扩大,已有的刚塑性 解在一定载荷强度范围内不能准确预报钢梁的实际位移。     

基于饱和响应时间的封闭空间内爆炸载荷等效方法研究

针对舱内爆炸载荷形式复杂、作用时间长、缺乏有效的简化描述方法的问题，首先采用显式动力学计算程序开展了内爆载荷作用下钢板动态响应的数值计算，在与试验结果对比验证的基础上分析了金属板的内爆载荷饱和冲量。通过对216种不同爆炸载荷加载时长与金属板响应关系的分析，提出了内爆炸载荷作用下结构最大变形所对应的饱和时间计算经验公式，并给出了饱和时间的无量纲系数建议值。考虑到内爆载荷初始冲击波的影响，结合爆炸载荷饱和作用时间的规律，提出了封闭空间爆炸载荷的矩形载荷等效方法，对比了18组简化载荷与耦合载荷分别作用下钢板的动力响应，验证了等效方法的有效性。     

厚壁圆筒的安定分析

本文讨论了幂强化材料以及弹性—幂强化材料厚壁圆筒在循环内压作用下的安定性;介绍了机动安定定理的推理以及具有部分恒定载荷时的表达式;讨论了厚壁圆筒在恒定内压与循环温度作用下的安定性。     

应变控制的热机械疲劳行为的数值模拟

根据高温合金材料的力学性能，以弹粘塑性本构模型为基础，用数值模拟方法研究材料的热机械疲劳循环特性，模型将应变分为弹性应变、温度应变和粘塑性应变三部分，认为材料在高温循环载荷下呈现明显的弹粘塑性特征，根据虚位移原理建立轴对称体的弹粘塑性计算有限元格式，对于循环机械载荷和循环温度载荷，程序中采用了增量法迭代求解，在非线性项中不仅考虑了机械载荷增量的影响，同时也考虑了温度增量的影响，根据应变控制热机械疲劳的特点，发展了应变增量法的有限元计算方法、通过数值模拟，得到材料在各种循环载荷下的应力—应变响应，数值模拟较好地反映了粘塑性变形过程以及温度变化的效应，所描述的不可逆系统在某一时刻的状态完全由当时的状态参数、内变量、承载时间及塑性应变累积量决定，对带缺口试件的模拟结果显示了程序对复杂轴对称结构进行热机械疲劳计算的有效性。     

基于双剪统一强度理论的厚壁圆筒塑性极限载荷分析

应用双剪统一强度理论,考虑材料的拉压异性和同性,推导了在内压和轴力联合作用下的厚壁圆筒的塑性极限载荷表达式．在该表达式中,当其系数取不同的值时,就能得到按Tresca屈服准则、线性逼近的Mises屈服准则和双剪应力屈服准则进行计算的结果．     

拉压性能不同对厚壁圆筒安定性的影响

一些材料在拉伸和压缩时的性能有明显的不同，这一性质会对循环载荷作用下的结构的安定性产生影响．本文以承受内压的厚壁圆筒为例，分析了拉压不同情况下结构安定性的规律．     

编织Kevlar/Epoxy复合材料层合板在冲击荷载下的动态响应

通过编织Kevlar/Epoxy复合材料层合板的平头弹冲击实验，分析了结构在不同冲量下的变形失效模式以及结构的抗冲击性能。实验表明复合板的变形失效模式主要表现为:(1)弹性变形；(2)复合板表面嵌入失效及整体塑性大变形；(3)背面纤维拉伸断裂及分层失效。基于实验研究，运用LS-DYNA 971有限元程序对铺层数不同的复合板在冲击载荷作用下的动态响应过程进行了数值模拟，模拟结果与实验吻合较好，子弹作用区域边缘处首先发生近似圆形的嵌入失效，而在板背面发生近似正方形的破坏区域；计算中重点分析了铺层数对结构动力响应的影响，在一定冲量范围内，通过对铺层数的优化，能够有效地减小后面板挠度，提高结构的能量吸收效率，增强结构的抗冲击性能。     

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.