层合板自由振动和强迫振动的三维精确解

主要基于三维弹性力学和状态空间法给出了四边简支各向同性矩形层合板自由振动和强迫振动问题的精确解.首先基于三维弹性力学建立了层合板的基本方程,利用状态空间法解决了层合板的自由振动问题,然后根据Lagrange动力学方程求解了层合板受到横向冲击时的强迫振动响应

高超声速飞行器热防护材料与结构的研究进展

高超声速飞行器是航空航天的一个重要发展方向,在未来国防安全中起着重要作用.高超声速飞行器热防护材料与结构是高超声速飞行器设计与制造的关键技术之一,它关系到飞行器的安全.高超声速飞行器热防护材料与结构主要有金属TPS热防护系统、超高温陶瓷、C/C复合材料等.从材料制备、抗氧化、力学与物理性能表征等方面综述了热防护材料与结构的研究与应用现状,评述了其发展趋势

高超音速飞行器及其关键技术简论

简要评述了高超音速飞行器及其关键技术,包括:高超音速飞行的定义、高超音速流动的特征、高超飞行覆盖范围、高超飞行器蒙皮温度、以及高超飞行设计特点;高超飞行器的背景;高超飞行器研制的发展简史,及经验与思考;吸气式高超飞行器典型设计过程、发展战略、技术规划、和关键技术领域

轻质多孔材料研究进展

高超声速武器是军事装备的发展方向,在未来战争中起着重要作用。轻质材料是高超声速飞行器设计与制造的关键技术之一,它是实现高超声速飞行器高超声速、高机动性、远程打击等性能的基础和保障。高超声速飞行器轻质材料主要有蜂窝材料、泡沫金属材料、点阵材料。这些材料具有超轻、高比强、高比刚度、高强韧、高能量吸收等优良机械性能,以及减震、散热、吸声、电磁屏蔽等特殊性质,它兼具功能和结构双重作用,是一种性能优异的多功能材料。本文从材料制备、结构设计、力学与物理性能表征等方面综述了高超声速飞行器轻质材料的研究与应用现状,比较了三种轻质材料的机械和物理性能,重点评述了新型点阵材料的制备工艺、结构构型、力学及其他性能,指出了其发展趋势

学术期刊国际化刍议

自然科学学术刊物的基本职能:一是记录册,二是信息源。学术刊物刊登创新的学术论文,是人类认识自然界的历史记录,是科学的信息源,是人类进一步认识世界的武库。科学无国界,记录科学创新成果与进步的学术刊物也是无国界的。自然科学的创新成果,都是国际性的。世界上每一个学术刊物,都是世界科学宝库中的一员

双层金属纳米板界面能密度的尺寸效应

界面能密度是表征纳米复合材料与结构界面力学性质的重要物理量.采用分子动力学方法计算了不同面心立方金属晶体构成的双材料纳米薄板结构的界面能密度，分析了界面晶格结构形貌变化及界面效应对原子势能的影响.结果表明：双材料纳米薄板界面具有周期性褶皱状疏密相间的晶格结构形貌，界面上原子势能亦呈现周期性分布特性，而靠近界面的两侧原子势能与板内原子势能具有明显差异.拉格朗日界面能密度和欧拉界面能密度均随双层薄板厚度的增加而增加，最终趋向于块体双材料结构的界面能密度

Tunable Adhesion of a Bio-Inspired Micropillar Arrayed Surface Actuated by a Magnetic Field

Bio-inspired functional surfaces attract many research interests due to the promising applications. In this paper, tunable adhesion of a bio-inspired micropillar arrayed surface actuated by a magnetic field is investigated theoretically in order to disclose the mechanical mechanism of changeable adhesion and the influencing factors. Each polydimethylsiloxane (PDMS) micropillar reinforced by uniformly distributed magnetic particles is assumed to be a cantilever beam. The beam's large elastic deformation is obtained under an externally magnetic field. Specially, the rotation angle of the pillar's end is predicted, which shows an essential effect on the changeable adhesion of the micropillar arrayed surface. The larger the strength of the applied magnetic field, the larger the rotation angle of the pillar's end will be, yielding a decreasing adhesion force of the micropillar arrayed surface. The difference of adhesion force tuned by the applied magnetic field can be a few orders of magnitude, which leads to controllable adhesion of such a micropillar arrayed surface. Influences of each pillar's cross section shape, size, intervals between neighboring pillars, and the distribution pattern on the adhesion force are further analyzed. The theoretical predictions are qualitatively well consistent with the experimental measurements. The present theoretical results should be helpful not only for the understanding of mechanical mechanism of tunable adhesion of micropillar arrayed surface under a magnetic field but also for further precise and optimal design of such an adhesion-controllable bio-inspired surface in future practical applications

Surface effect in axisymmetric Hertzian contact problems

Surface effect in three different axisymmetric Hertzian contact models is investigated in this paper with a recently developed elastic theory for nanostructured materials, including a Boussinesq problem, contact problem between a rigid flat-ended cylindrical indenter and an elastic half space as well as contact problem between a rigid spherical indenter and an elastic half space. With the help of the Love's strain function method and Hankel integral transformation, closed-form solutions of the stress and displacement fields at the surface of an elastic half space subjected to a concentrated force are achieved, based on which the interface tractions and displacements in the three different axisymmetric contact problems can be further obtained. It is found that surface effect in these contact problems can be characterized only by an intrinsic length, i.e., the ratio of the bulk surface energy density to the bulk shear modulus of the indented material. When the contact radius is comparable with the intrinsic length, surface effect is much obvious, leading to a serious deviation between the two solutions predicted respectively by the theoretical model developed for nanomaterials and the classical contact model. A more interesting phenomenon is about surface effect on the indentation hardness, which is found to increase with the reduction of the indenter radius when the external load is fixed, or to increase with the decrease of the external load when the indenter radius keeps unchanged. All the results in this paper should be helpful not only for deep understanding of the surface effect on nano-contact behaviors but also for further revealing the nature of surface effect of nano-indentation hardness. (C) 2018 Elsevier Ltd. All rights reserved

Influencing factors of droplet aggregation on hierarchical wedge-shaped functional surfaces

Spontaneous droplet aggregation has great potential applications in liquid transportation, droplet-based microfluidics and water collection in deserts. Several novel hierarchical functional surfaces have been well prepared experimentally, on which small droplets would aggregate to form large droplets. The common feature of the hierarchical surface is wedge-shaped functional zone. However, how to guarantee the stability of water collecting function in real design and application is still lack of theoretical guidance. Based on molecular dynamics simulations, numerical experiments are systematically carried out in the present paper. Several important influencing factors of droplet spontaneous aggregation are studied. It is found that three typical size-dependent moving patterns of droplets may exist on such a hierarchical functional surface, i.e. lingering, pinning and directional transporting. The physical mechanism is further revealed for each pattern in terms of potential energy, which significantly depends on the wedge angle, direction of the wedge and symmetry of the bifurcation of each level. In order to achieve spontaneous droplet aggregation effectively, three conditions need to be met a relatively small wedge angle at each level, wedges in the same direction at different levels, and asymmetric arrangement of wedges at the same level. A three-level functional surface is further numerically designed, which can realize water collection successfully. The results in this paper should be useful for the precise design of hierarchical functional surfaces of water collection in practical application