电活性聚合物圆柱壳静态与动态电压下的响应及稳定性

摘要：在电活性聚合物圆柱壳内外表面施加电压,圆柱壳会变薄并且伸长,因此相同的电压会在圆柱壳内产生更大的电场。这个正反馈可能使圆柱壳厚度不断变薄,最终导致其失稳破坏。本文研究了电活性聚合物圆柱壳在静态和周期电压作用下的响应及稳定性问题。采用neo-Hookean材料模型得到描述圆柱壳表面运动的非线性常微分方程。给出了圆柱壳在不同厚度和边界条件下外加电压随圆柱壳变形的变化曲线,结果表明存在一个临界电压,当外加电压大于这一临界值时,圆柱壳将被破坏。同时,也讨论了厚度和边界条件对临界电压的影响。圆柱壳在正弦周期电压作用下,其运动随时间的变化是周期性的或拟周期性的非线性振动。给出了圆柱壳振动固有频率的计算结果,采用打靶法得到圆柱壳振动的周期解,并且用数值法研究了周期解的稳定性。采用数值仿真得到圆柱壳振动振幅随外加动态电压激励频率的变化曲线,结果表明圆柱壳会发生多频共振,共振时圆柱壳振幅发生跳跃,导致圆柱壳失稳破坏。最后给出共振点临近点的振动曲线和相图,并对其振动特性进行讨论。     

开孔泡沫铝填充圆管的准静态压缩行为

采用开孔结构泡沫铝填充到薄壁圆形铝管中,制备出开孔泡沫铝夹芯铝管,并进行压缩实验,研究了这种结构材料的压缩力学行为和变形特征以及材料的结构特征参数对压缩力学性能和能量吸收特性的影响。在压缩过程中,泡沫铝夹芯铝管的载荷-位移曲线呈现出弹性段、波动的屈服平台段和压实段3个阶段特征;铝管的径厚比及泡沫铝本身的参数和强度对填充管的屈服强度、平均压溃力和吸能特性均有着非常显著的影响。填充泡沫铝后铝管的压缩变形方式发生改变,管壁只发生向外翻折变形,产生的环状褶皱减少。     

An eigen theory of static electromagnetic field for anisotropic media

Static electromagnetic fields are studied based on standard spaces of the physical presentation, and the modal equations of static electromagnetic fields for anisotropic media are derived. By introducing a new set of first-order potential functions, several novel theoretical results are obtained. It is found that, for isotropic media, electric or magnetic potentials are scalar; while for anisotropic media, they are vectors. Magnitude and direction of the vector potentials are related to the anisotropic subspaces. Based on these results, we discuss the laws of static electromagnetic fields for anisotropic media.     

On the truth of nanoscale for nanobeams based on nonlocal elastic stress field theory： equilibrium, governing equation and static deflection

This paper has successfully addressed three critical but overlooked issues in nonlocal elastic stress field theory for nanobeams： （i） why does the presence of increasing nonlocal effects induce reduced nanostructural stiffness in many, but not consistently for all, cases of study, i.e., increasing static deflection, decreasing natural frequency and decreasing buckling load, although physical intuition according to the nonlocal elasticity field theory first established by Eringen tells otherwise？ （ii） the intriguing conclusion that nanoscale effects are missing in the solutions in many exemplary cases of study, e.g., bending deflection of a cantilever nanobeam with a point load at its tip; and （iii） the non-existence of additional higher-order boundary conditions for a higher-order governing differential equation. Applying the nonlocal elasticity field theory in nanomechanics and an exact variational principal approach, we derive the new equilibrium conditions, do- main governing differential equation and boundary conditions for bending of nanobeams. These equations and conditions involve essential higher-order differential terms which are opposite in sign with respect to the previously studies in the statics and dynamics of nonlocal nano-structures. The difference in higher-order terms results in reverse trends of nanoscale effects with respect to the conclusion of this paper. Effectively, this paper reports new equilibrium conditions, governing differential equation and boundary condi- tions and the true basic static responses for bending of nanobeams. It is also concluded that the widely accepted equilibrium conditions of nonlocal nanostructures are in fact not in equilibrium, but they can be made perfect should the nonlocal bending moment be replaced by an effective nonlocal bending moment. These conclusions are substantiated, in a general sense, by other approaches in nanostructural models such as strain gradient theory, modified couple stress models and experiments.     

一维六方准晶中椭圆孔边裂纹的静态与动态分析

通过构造保角映射函数,借助复变函数方法,研究了一维六方准晶中椭圆孔边裂纹的反平面剪切问题,给出了Ⅲ型裂纹问题的应力强度因子的解析解.当椭圆的长、短半轴以及裂纹长度变化时,所得结果不仅可以还原为Griffith裂纹的情形,而且得到孔边裂纹问题、T型裂纹问题和半无限平面边界裂纹问题的应力强度因子的解析解.就声子场而言,这些解与经典弹性的结果完全一致.接着对椭圆孔边裂纹的动力学问题进行了研究,并得到了Ⅲ型动态应力强度因子的解析解.当裂纹速度V→0时,动力学解还原为静力学解.这些解在科学与工程断裂中有着潜在的应用价值.     

甲烷水合物在静态体系中生成反应的促进

静态体系生成甲烷水合物是个缓慢的、不完全的过程。即使使用表面活性剂也不能实现反应物的100％转化。本文讨论了在静态反应停止后,使用系统温度振荡的方法来促进水合反应的继续进行,直至完全转化。在系统温度从-10～4℃之间周期振荡时,原本停滞的水合反应在水的相变温度附近又开始发生反应,由于水合物合成时铠甲效应的存在,水在样品中的过冷度达到10℃左右。文中对样品的热物性测试表明,在经过几个温度变化周期后,反应非常完全,反应器中样品是100％的甲烷水合物。     

硬盘抗冲击振动特性的研究进展

硬盘驱动器是计算机最重要的外存储设备.由于硬盘抗冲击振动问题的重要性和复杂性,许多研究者对此问题从各个方面进行了研究.本文从硬盘的基本结构和工作原理入手,介绍了磁头/磁盘系统的静动态特性,分析了影响磁头/磁盘系统性能的重要因素及其原理,并对国内外有关提高硬盘抗冲击振动性能的研究进行了较为系统的回顾和分析,最后阐述了硬盘冲击振动的控制研究,分析了硬盘目前所面临的关键问题及其可能的解决方案.     

Nonlinear static and dynamic responses of an electrically actuated viscoelastic microbeam

On the basis of the Euler-Bernoulli hypothesis, nonlinear static and dynamic responses of a viscoelastic microbeam under two kinds of electric forces [a purely direct current （DC） and a combined current composed of a DC and an alternating current] are studied. By using Taylor series expansion, a governing equation of nonlinear integro-differential type is derived, and numerical analyses are performed. When a purely DC is applied, there exist an instantaneous pull-in voltage and a durable pull-in voltage of which the physical meanings are also given, whereas under an applied combined current, the effect of the element relaxation coefficient on the dynamic pull-in phenomenon is observed where the largest Lyapunov exponent is taken as a criterion for the dynamic pull-in instability of viscoelastic microbeams.     

遥感相机实验室静态MTF测量误差分析

应用于航空航天等军工技术领域的高分辨率遥感相机在轨图像处理过程中,需要用到相机实验室静态MTF测量结果进行补偿复原,因此对其测量的准确性提出了较高的要求。针对目前遥感相机实验室静态MTF测量常用的固有频率目标法,进行了各相关误差源的深入量化分析,并结合某航天遥感相机的MTF测量计算出各误差源的影响程度,其中系统总误差和随机总误差分别为0.021 32和0.003 04,最后给出了提高测量精度的建议。在实际工程中,可根据测量条件估算出误差值,并对影响较严重的误差因素采取相应措施,从而提高测量的准确性,对遥感相机在轨图像处理有指导意义。