世界铁路发展状况及其关键力学问题 全国结构工程学术会议特邀报告

论述了世界部分发达国家和我国铁路发展情况、铁路运输的优点及其在经济建设中所发挥的作用。介绍了世界发达国家和我国铁路发展历史和未来轨道交通发展方向。详细讨论了现有铁路运输存在的问题和未来高速铁路亟待解决的关键力学问题。它们主要是:(1)弓网/列车/轨道(桥梁)大系统耦合动力学; (2)车辆结构强度和可靠度问题;(3)轮轨关系(脱轨、粘着、滚动接触疲劳和波浪形磨损、轮轨噪声);(4)高速列车弓网动力学和高速受流条件下摩擦磨损;(5)轨道结构关键力学和严酷环境下轨道工程破坏问题。这些问题直接危及到行车的安全和运行品质.并提出今后解决这些问题的主要方向。     

Algorithms for the analysis of 3D finite strain contact problems

From the constraint imposition aspects in 3D to friction regularization, various ideas are exposed in this paper. A variation of the Rockafellar Lagrangian is proposed which results in continuous second‐order derivatives if Lagrange multiplier estimates are greater or equal than one. This fact allows the adoption of a full second‐order (i.e. Lagrange–Newton) method avoiding sequential unconstrained minimization techniques. An algorithm for global and local contact detection is presented which is developed for dealing with large step sizes typical of implicit methods. A modified constraint definition to deal with non‐smooth situations is presented. Aspects of friction implementation, including a regularization scheme which ensures stepwise objectivity, are detailed. Finally, several illustrative examples are carried out with success. Copyright © 2004 John Wiley & Sons, Ltd.     

Multidimensional Kinetics of Nucleation in Liquid-Vapor Systems

A metastable system is described as an ensemble of locally isolated statistically independent centers, with a possibility of one and only one nucleus of a close-to- critical radius emerging on each one of these centers. It is assumed that this event occurs as a result of fluctuations in a heterophase subsystem and leads to the formation of a viable nucleus at a given point in space. The process of the emergence of this nucleus is treated as the first crossing of the potential barrier by a Brownian particle. Proceeding from the principles of nonequilibrium thermodynamics, dynamic equations of bubble (droplet) growth are derived, which correspond to the Onsager relations. These formulas are used as Langevin equations in multidimensional phase space and are related to the respective Fokker-Planck equation whose solution enables one to determine the local rate of emergence of a viable nucleus and, as a consequence, the rate of its emergence in the entire system. An alternative expression is given for the rate of homogeneous steady-state nucleation, which differs from the classical expression by the pre-exponential factor and, in the case where one parameter (radius) may be sufficient, gives close limits of attainable superheat (supersaturation). Given the expression for the nonequilibrium work of bubble (droplet) and the distribution of heterogeneous centers, the obtained result may be readily generalized to the case of heterogeneous nucleation.     

喷射成形CuCr25合金触头材料的制备及致密化处理

利用喷射成形技术制备了CuCr2 5合金触头材料 ,研究了雾化压力对显微组织、致密度和收得率的影响 ,对制得的沉积坯件进行了热锻压和热等静压致密化处理 ,并测试了触头材料的密度、硬度和电导率。研究结果表明 :最合适的雾化压力为 0 .6MPa ,沉积坯件经过 95 0℃锻压后再在 10 70℃ ,2 0 0MPa下热等静压 8h ,可以得到全致密的触头材料 ,铬颗粒平均直径小于 10 μm ,硬度达 10 0HB ,电导率 2 5～2 9Ms·m- 1 ,说明致密化处理后的喷射成形CuCr2 5合金是一种优良的触头材料。     

Au/Ni/Al/Ti/AlxGa1-xN/GaN和Au/Pt/Al/Ti/AlxGa1-xN/GaN欧姆接触研究

研究并对比了Ti/Al/Ni/Au和Ti/Al/Pt/Au多层金属膜与未掺杂的Al0 .2 2 Ga0 .78N/GaN(i AlGaN/GaN)异质结构之间的欧姆接触性质。在退火温度低于 70 0℃时 ,两种接触样品上都不能得到欧姆接触。随着退火温度的升高 ,85 0℃快速退火后 ,在Ti/Al/Ni/Au接触上获得了 1.2 6×10 - 6 Ω·cm2 的比接触电阻率 ,在Ti/Al/Pt/Au接触上获得了 1.97× 10 - 5Ω·cm2 的比接触电阻率。研究结果表明 ,金属与半导体接触界面和Al0 .2 2 Ga0 .78N异质结构界面载流子沟道之间适当的势垒的存在对高质量欧姆接触的形成起重要作用 ,势垒的宽度取决于退火温度以及退火的具体进程。对Ti/Al/Ni/Au和Ti/Al/Pt/Au欧姆接触比接触电阻率的差异进行了解释。     

Low-velocity impact analysis of composite laminates using linearized contact law

Usually many researchers have used the modified Hertzian contact law or experimental static indentation law to analyze impact response of composite laminates subjected to low-velocity impact. In this study, physical meaning of the analytical method using the laws was investigated and the difference between the analytical results obtained using the two laws was also investigated. Furthermore parametric study on contact coefficient and exponent of the contact law was performed. Finally it could be shown that linearized contact law could be well applied to the low-velocity impact analysis of composite laminates. If this concept is used, any general-purpose finite element method software can be used to solve impact problem without direct developing any FEM code by each researcher. In this paper, some analytical results analyzed using a general-purpose commercial FEM software were also presented.     

The Study of Low Surface Energy Fluorocarbon Coatings with Fluor Content Being Lower

A kind of low surface energy fluorocarbon coatings from the synthesized fluoro-acrylic resin was developed.The molecule orientation principle of nonpolar and polar functional groups in the coatings was analyzed. The contact angles of pure water drops on the surfaces of various fluoro-monomer homopolymers and interpolymers were measured. The relation of coatings' fluoro-content with the surface energy was determined. The distribution of fluoric functional groups in the coatings was investigated. The test results show that though the total content of fluor of the fluorocarbon coatings is relative few, their surface energy is really low due to the enrichment of fluoro-chains on the surfaces.     

用连续接触模型预测平面连杆机构转动副的分离

本文采用平面连杆机构有间隙转动副的连续接触模型，来计算机构周期运动时的间隙副的运动反力，由间隙杆受压来预测实际的含间隙的运动副在机构周期运动时是否会发生分离。本文以一平面四杆机构为例说明了该方法。     

舰船防护结构穿甲后爆炸的数值仿真分析

为了研究冲击爆炸作用下舰船防护结构的破坏情况,将该结构简化为多层板架结构,借助于有限元程序LS-DYNA中的ALE算法,同时考虑穿甲和爆炸的作用,对其在穿甲后爆炸荷载作用下的非线性动态响应过程进行仿真分析,描述了钢板的破口形状、破口半径及板上单元等效应力随时间变化的情况,并与舷外接触爆炸对结构的破坏情况进行比较.结果表明穿甲后爆炸能对舰体内部造成破坏,因此它是一种比较理想的反舰攻击方式.     

钙处理时机对LF-RH精炼过程Al2O3基夹杂物的影响

为研究LF-RH精炼工艺生产Q690钢时不同钙处理时机下夹杂物特征的变化,开展工业试验对RH精炼前后钙处理炉次取样进行定量分析对比。钙处理后夹杂物中CaO质量分数持续增加,CaS质量分数瞬态增加,夹杂物熔点降低。RH精炼前钙处理炉次中,RH精炼过程夹杂物的成分接近低熔点区,结束时夹杂物数量密度和面积分数分别为15个/mm2和0.01%。RH精炼后钙处理炉次中,RH精炼过程夹杂物依旧为高熔点Al₂O₃-MgO类型,结束时夹杂物数量密度和面积分数分别降至1个/mm2和0.002 5%。RH精炼前钙处理会使RH精炼过程夹杂物熔点以及夹杂物与钢液间的接触角降低,导致夹杂物去除驱动力降低,从而抑制夹杂物的去除。因此LF-RH精炼工艺生产铝脱氧钢时,为提高精炼过程钢中非金属夹杂物的去除效率,应在RH精炼后进行钙处理操作。