非晶态固体的结构可以决定性能吗?

晶态固体的力学性能与塑性变形主要由结构缺陷, 比如位错的运动决定. 而在非晶态固体中结构如何决定性能, 仍然是固体力学、材料学和凝聚态物理学共同关心但尚未解决的核心问题之一.传统材料学研究的经典范式为"结构决定性能". 遵循这一信条, 已经有大量的实验表征与理论、模拟研究, 尝试将非晶态固体的某种结构特征与性能建立一一对应关系. 但是, 科学界对于非晶固体结构-性能关系成立与否, 以及背后隐藏的规律知之甚少. 本文针对非晶态固体的变形机制以及其微结构特征, 基于分子动力学模拟, 定量评估短程简单结构与中长程复杂结构在决定非晶态固体动力学性能方面的效用. 通过海量抽样每种具体玻璃结构的激活能(标识激发难易程度), 尝试将结构参数与激活能建立定量关系, 从而揭示出非晶态固体结构-性能关系的隐藏主控因素为结构的空间关联, 受限比几何结构本身更关键. 只有某种结构在空间上呈现亚纳米级的空间关联长度, 这种完备结构才有可能有效地决定非晶态固体的力学性能, 而短程简单结构则无效. 进一步, 给出了评价非晶态固体结构预测性能有效性的普适定量方法, 为建立广义无序物质的结构-性能关系提供了筛选准则.      

工程科学前沿的拓荒者——郑哲敏

郑哲敏先生是著名力学家, 我国爆炸力学的奠基人和开拓者, 2012年度国家最高科学技术奖获得者. 本文回顾了郑哲敏先生在过去60多年中非常丰富的科研活动, 特别是他在爆炸加工、地下核爆、爆炸排淤、穿破甲、煤与瓦斯突出、水合物开采、水弹性动力学、材料力学行为等方面的杰出学术贡献. 这些工作闪耀着鲜明的工程科学特点, 即着眼国家重大需求, 从错综复杂的问题中概括提炼关键物理因素, 创新理论, 进而指导实践. 郑哲敏先生的科学贡献和学术思想, 对于力学学科发展, 有着重要的现实意义和参考价值.     

凹凸棒土增强聚丙烯复合材料冲击断裂韧性的研究

 用Charpy冲击实验装置研究凹凸棒土（AT）增强聚丙烯（PP）复合材料的断裂韧性。测量AT含量为10wt%~40wt%试样的断裂韧性。结果显示，在AT含量为10wt%~30wt%范围内，复合材料的断裂韧性（G_c）高于纯基体PP．这说明，在一定条件下，加入AT可以改善PP的断裂韧性。     

Comparative study of amorphous and crystalline Zr-based alloys in response to nanosecond pulse laser ablation

In shock tube experiments, the interaction between the reflected shock and boundary layer can induce shock bifurcation and weak ignition. The weak ignition can greatly affect the ignition delay time measurement in a shock tube experiment. In this work, two-dimensional simulations considering detailed chemistry and transport are conducted to investigate the shock bifurcation and non-uniform ignition behind a reflected shock. The objectives are to interpret the formation of shock bifurcation induced by the reflected shock and boundary layer interaction and to investigate the weak ignition and its transition to strong ignition for both hydrogen and dimethyl ether. It is found that the non-uniform reflection of the incident shock at the end wall produces a wedge-shaped oblique shock foot at the wall. The wedge-shaped structure results in strong interactions between reflected shock and boundary layer, which induces the shock bifurcation. It is demonstrated that the local high-temperature spots at the foot of the bifurcated shock is caused by viscous dissipation and pressure work. As the post-reflected shock temperature increases, the transition from weak ignition to strong ignition in a stoichiometric hydrogen/oxygen mixture is observed. The relative sensitivity of ignition delay time to the post-reflected shock temperature is introduced to characterize the appearance of weak ignition behind the reflected shock. Unlike in the hydrogen/oxygen mixture, weak ignition is not observed in the stoichiometric dimethylether/oxygen mixture since it has a relatively longer ignition delay time and smaller relative sensitivity.

     

A generalized self-consistent Mori-Tanaka model for predicting the effective moduli of the coated inclusion based composite materials

The weak point of the generalized self-consistent method (GSCM) is that its solution for the effective shear moduli involves determining the complicated displacement and strain fields in constitutents. Furthermore, the effective moduli estimated by GSCM cannot be expressed in an explicit form. Instead of following the procedure of GSCM, in this paper a generalized self-consistent Mori-Tanaka method (GSCMTM) is developed by means of Hill's interface condition and the assumption that the strain in the inclusion is uniform. A comparison with the existing theoretical and experimental results shows that the present GSCMTM is sufficiently accurate to predict the effective moduli of the coated inclusion-based composite materials. Moreover, it is interesting to find that the application of Hill's interface condition in volumetric domain is equivalent to the Mori-Tanaka average field approximation. This project was supported by the National Natural Science Foundation of China and China Postdoctoral Science Foundation.     

广义自洽Mori-Tanaka模型及涂层夹杂体复合材料的有效模量

经典广义自洽模型的最大不足是需要确定相材料的位移及应变场,这一过程十分繁杂,而且最后得到的有交剪切模量无法显式表达难以应用,该文摈弃这一经典做法,而从广义自洽模型的应变等价条件出发,在夹杂应变均匀的近似假定下,将Ｈｉｌｌ界面条件应用于整个二相体内,从而得到一种可以预报涂层夹杂体复合材料有效模量的广义自洽Ｍｏｒｉ－Ｔａｎａｋａ模型,与已有的实验及理论的比较表明,该模型准确可靠,而且有效体积和剪切模量     

DYNAMIC MECHANICAL BEHAVIOR AND PENETRATION PERFORMANCE OF WFeNiMo HIGH-ENTROPY ALLOY 1)

为了探究不同应变速率下WFeNiMo高熵合金的变形行为和侵彻性能, 采用万能材料试验机、分离式霍普金森压杆开展了高熵合金的静动态力学性能试验, 讨论了其在不同应变速率下变形特征微观机制. 基于弹道枪试验平台开展了高熵合金与典型钨合金(93W-4.9Ni-2.1Fe,wt%)破片对有限厚钢靶侵彻作用性能试验研究, 分析了两种合金破片侵彻作用过程与靶板破坏特征、侵彻穿孔能量消耗与撞击速度间的关系. 结果表明: 高熵合金、钨合金材料屈服强度与应变率呈正相关, 且在相同的应变率下高熵合金具有更高的屈服强度; 随着应变率的提高, 高熵合金由脆性断裂、韧脆混合的准解理断裂发展至具有黏着特性的破碎变形模式; 高熵合金具有较强的局部绝热变形能力, 在侵彻薄钢靶时体现出较高的剪切敏感性; 相同撞击速度下, 高熵合金破片穿靶消耗的能量低于钨合金破片, 对于薄钢靶具有更强的侵彻穿透能力. 高熵合金具有优异的力学性能和侵彻能力, 在高速撞击薄靶板时除了传统的剪切冲塞作用还具有一定的能量释放特性, 在预制破片上有较好的应用前景.     

An explicit expression of the effective moduli for composite materials filled with coated inclusions

The obvious shortcoming of the generalized self-consistent method (GSCM) is that the effective shear modulus of composite materials estimated by the method can not be expressed in an explicit form. This is inconvenient in engineering applications. In order to overcome that shortcoming of GSCM, a reformation of GSCM is made and a new micromechanical scheme is suggested in this paper. By means of this new scheme, both the effective bulk and shear moduli of an inclusion-matrix composite material can be obtained and be expressed in simple explicit forms. A comparison with the existing models and the rigorous Hashin-Shtrikman bounds demonstrates that the present scheme is accurate. By a two-step homogenization technique from the present new scheme, the effective moduli of the composite materials with coated spherical inclusions are obtained and can also be expressed in an explicit form. The comparison with the existing theoretical and experimental results shows that the present solutions are satisfactory. Moreover, a quantitative comparison of GSCM and the Mori-Tanaka method (MTM) is made based on a unified scheme. The project supported by the National Natural Science Foundation of China under the Contract NO. 19632030 and 19572008, and China Postdoctoral Science Foundation     

REVIEW OF THE THIRD NATIONAL SYMPOSIUM ON EXPLOSION AND IMPACT DYNAMICS FOR YOUNG SCHOLARS$^{\bf 1)}$

简要介绍了第三届全国爆炸与冲击动力学青年学者学术研讨会的情况,概况总结了与会学者所做的报告内容. 报告包括 4 个特邀报告、19 个专题邀请报告和 17 个主题邀请报告,其中主题邀请报告分为爆轰和爆炸动力学、结构动力学和多尺度高性能计算、材料动力学和实验测试技术、复合材料结构的动态力学行为、轻质结构的吸能特性和优化设计等 5 个主题. 研讨会为从事爆炸与冲击动力学的青年学者开展学术交流、建立学术友谊、增强学术合作提供了优秀平台,对学科的建设和发展起到了积极推进作用.     

液体的fragility及其与玻璃固体力学性能的关联

Angell在20世纪80年代提出的液体fragility概念, 为认识玻璃态本质打开了一扇新的窗口, 是联系玻璃形成液体和固体的纽带. 目前, 玻璃转变的主流理论(如模态耦合理论、势能形貌等)围绕fragility展开的研究已经成为玻 璃科学领域的一个热点; fragility与玻璃固体基本力学性能之间的关联研究为力学工作者开辟了一片新的研究领 域.本文将就玻璃态转变相关基本现象、表征玻璃态转变动力学行为的代表性理论、液体 fragility与玻璃固体力学性能关联研究现状进行分析评述, 并就本领域今后值得关注的问 题进行展望.