Theoretical and experimental researches of size effect in micro-indentation test

Micro-indentation tests at scales on the order of sub-micron have shown that the measured hardness increases strongly with the indent depth or indent size decreasing, which is frequently referred to as the size effect. However, the trend is at odds with the size-independence implied by conventional elastic-plastic theory. In this paper, strain gradient plasticity theory is used to model the size effect for materials undergoing the micro-indenting. Meanwhile, the micro-indentation experiments for single crystal copper and single crystal aluminum are carried out. By the comparison of the theoretical predictions with experimental measurements, the micro-scale parameter of strain gradient plasticity theory is predicted, which is fallen into the region of 0.8–1.5 micron for the conventional metals such as copper (Cu), aluminum (Al) and silver (Ag). Moreover, the phenomena of the pile-up and sink-in near micro-indent boundary are investigated and analyzed in detail.     

推进剂的撞击损伤状态对其燃烧转爆轰的影响

设计加工了燃烧转爆轰的实验装置,并建立了相应的测试系统,旨在研究NEPP推进剂颗粒装药的燃烧转爆轰形成机理。并以大型落锤为加载手段,撞击NEPP推进剂试样,经实验发现,损伤明显地促进了颗粒装药燃烧向爆轰的转变,增加了该推进剂使用的危险性。     

多孔和铸装高能推进剂的燃烧转爆轰

为研究多孔和铸装高能推进剂的危险性能 ,设计加工了燃烧转爆轰的实验装置 ,并建立了以光电管为主的测试系统。经实验发现 ,多孔装药在燃烧向爆轰的转变过程中有冲击波 /爆轰波的回传现象 ,而铸装药则没有。     

从"哥伦比亚"号悲剧看多尺度力学问题

航空航天安全蕴含着大量的涉及多个物理层次的多尺度力学问题．多尺度力学问题对现有的力学概念和理论是一个巨大的挑战、以铝合金层裂和岩石脆性破坏为典型案例,讨论了多尺度力学问题的特点、难点以及可能的处理方法,说明合理表征和处理多尺度问题的跨尺度耦合及跨尺度敏感性是解决多尺度问题的关键．     

国际理论和应用力学联合会全代会（IUTAM General Assembly）会议简介

1国际理论和应用力学联合会全代会的介绍 国际理论和应用力学联合会(IUTAM)全代会(Gen-eral Assembly)是全世界力学界的最高组织IUTAM的最高权力机构.全代会按照IUTAM诸参加国的等级(分5等)来划分代表名额.只有美国、日本等国由于交纳最高等级的会费而拥有5个代表名额,而我国在代表大会中有4位代表(郑哲敏,何友声,白以龙和杨卫).此外,在决策IUTAM     

SIZE EFFECT AND GEOMETRICAL EFFECT OF SOLIDS IN MICRO—INDENTATION TEST

Micro-indentation tests at scales of the order of sub-micron show that the measured hardness increases strongly with decreasing indent depth or indent size,which is frequently referred to as the size effect.At the same time,at micron or sub-micron scale,another effect,which is referred to as the geometrical size effects such as crystal grain size effect,thin flim thickness effect,etc.,also influences the measured material hardness.However,the trends are at odds with the size-independence implied by the conventional elastic-plastic theory.In the present research,the strain gradient plasticity theory(Fleck and Hutchinson)is used to model the composition effects(size effect and geometrical effect) for polycrystal material and metal thin film/ceramic substrate systems when materials undergo micro-indenting.The phenomena of the “pile-up“ and “sink-in“ apeared in the indentation test for the polycrystal materials are also discussed.Meanwhile,the micro-indentation experiments for the polycrystal Al and for the Ti/Si3N4 thin film/substrate system are carried out.By comparing the theoretical predictions with experimental measuremtns.the values and the variation trends of the micro-scale parameter included in the strain gradient plasticity theory are predicted.     

酚醛玻璃钢动态本构关系的实验研究

本文叙述了在轻气炮上作高速撞击实验,使用碳膜压阻传感器,一次记录多个应力历史波形,用Lagrange分析和路径线方法,求材料动态本构关系的方法。给出了应力在2 GPa、应变率4105S-1以下酚醛玻璃钢的数值形式本构关系。探讨了强应力脉冲在酚醛玻璃钢中传播衰减的物理原因。     

第二届苏联材料爆炸加工会议

由苏联科学院,国家科学技术委员会等六个单位联合举办的第2届苏联材料爆炸加工会议于1981年9月8日至10日在新西伯利亚科学城举行。中国、美国、西德、日本、印度、南斯拉夫、捷克、保加利亚、波兰等13个国家约50名外国代表应邀参加了这次会议。这是近15年来,中国科学工作者第二次参加苏联的国内学术会议。会议期间共发表了学术报告78篇。报告内容分 ...     

应力波在线性磁滞体中的衰减

通过对爆炸在岩石中产生的应力波的物理分析,判断岩石应力应变关系的磁滞效应可能是应力波在岩石中衰减的主要物理机制.在线性磁滞模型下,用拉氏变换和渐近展开方法,求得应力波传播的解析解.特别是得到了应力波头以方式衰减的应力波的特解.这种解所具有的一系列特性(波形自相似,波形特征,走时和半衰期的关系,动力学和运动学参量的峰值等)与实践观测结果及已有经验公式有相当好的一致性.并表明衰减指数l仅由磁滞参数α和参数Q确定,Q为无量纲应力波头导数的绝对值.因此,这个模型可作为进一步分析物理机制和建立经验公式的基础.     

Electrostatic Interactions Between Glycosaminoglycan Molecules

The electrostatic interactions between nearest-neighbouring chondroitin sulfate glycosaminoglycan (CS-GAG)molecular chains are obtained on the bottle brush conformation of proteoglycan aggrecan based on an asymptoticsolution of the Poisson-Boltzmann equation the CS-GAGs satisfy under the physiologicM conditions of articularcar tilage. The present results show that the interactions are associated intimately with the minimum separation distance and mutual angle between the molecular chains themselves. Further analysis indicates that the elec-trostatic interactions are not only expressed to be purely exponentiM in separation distance and decrease with the increasing mutual angle but also dependent sensitively on the sline concentration in the electrolyte solution within the tissue, which is in agreement with the existed relevant conclusions.