四阶边值问题正解的存在性与多解性

本文讨论了非线性四阶边值问题u^(4)(t)=φ（t）f(u(t),u“(t),t∈(0,1),u(0)=u(1)=u“(0) =u“(1)=0正确的存在性，其中φ（t)∈C([0,1],[0,∞)),f(u,v)∈C（[0,∞],[0,∞))。利用锥压缩与锥拉伸不动点定理，给出了该问题正解存在与多个正解存在的充分条件。     

熔锥型全波耦合器

从耦合模方程出发，分析了全光纤非对称熔融拉锥型耦合器的带宽特性，提出和论证了全波(O+E+S+C+L band)耦合器的制作方案，并且在工艺上实现了全波耦合，其带宽达到了390nm(1260—1650)，分束比1∶99；附加损耗01dB. 关键词： 全波耦合器 熔融拉锥 带宽 预拉伸     

水中Ag电极上取向与结构的SERS研究—不同电极电位和NaClO…

将特殊的ＯＲＣ方法、薄层溶液技术和差谱方法相结合，在较宽的电位区间（－０．７～－２．０Ｖ），将得了不含任何（类）卤素离子的ＮａＣｌＯ４／Ａｇ体系中水的ＳＥＲＳ谱，结果表明，不同浓度的ＮａＣｌＯ４体系中，尽管体相水的结构有很大差别，但电极表面的吸附水有相似的结构特征，即由于电场作用而使有序性较高，并且随电极电位电极负向零电荷电位变化时可能都经历着由单氢端吸附转变为双氢端吸附，继而又转向氧端吸附的取向     

Magnetocrystalline Anisotropy and Magnetoelasticity of Preferentially Oriented Martensitic Variants in Ni52Mn24Ga24 Single Crystals

The magnetocrystalline anisotropy and magnetoelasticity of preferentially oriented martensitic variants in an off-stoichiometric Ni52Mn24Ga24 single crystal have been investigated.We found that the easy magnetization direction of the martensite phase in the [110] direction,and the hard magnetization exhibited in [001],the growth direction of single crystals.The temperature dependence of the anisotropy fields and constants of Ni52Mn24Ga24 have been determined.It was found that,at the martensite phase,the anisotropy field increases monotonically with decreasing temperature,but the anisotropy constant first increases rapidly and then the increasing rate becomes smaller and smaller.Based on a previous model,the present results suggest that the competition between the Zeeman energy and the magnetocrystalline anisotropy energy is mainly responsible for the magnitude of magnetic-field-induced strain in this material.     

Analytical solution of magnetohydrodynamic sink flow

An analytical solution to the famous Falkner-Skan equation for the magnetohydrodynamic (MHD) flow is obtained for a special case, namely, the sink flow with a velocity power index of −1. The solution is given in a closed form. Multiple solution branches are obtained. The effects of the magnetic parameter and the wall stretching parameter are analyzed. Interesting velocity profiles are observed with reversal flow regions even for a stationary wall. These solutions provide a rare case of the Falkner-Skan MHD flow with an analytical closed form formula. They greatly enrich the analytical solution for the celebrated Falkner-Skan equation and provide better understanding of this equation.     

三维四向编织复合材料的拉伸尺寸效应研究

通过对三维四向碳/环氧编织复合材料的拉伸实验,观测了不同几何尺寸的试件的破坏模式和断口形貌,得到了材料在拉伸载荷下不同的破坏机理以及材料的力学性能与试件几何尺寸的相关性,研究表明材料随着内部单胞数量的增加材料的弹性模量递减,而剪切模量和泊松比递增的变化规律,通过体积平均法从理论上预报了材料的弹性性能,预报结果与实验结果相符,实验和理论所获结论为进一步进行材料的刚度和强度预报以及强度准则的建立奠定了必要的实验和理论基础.     

Gigacycle fatigue behaviors of two SNCM439 steels with different tensile strengths

Gigacycle fatigue behaviors of two SNCM439 steels with different tensile strengthes were experimentally studied by rotating bending tests,to investigate the effects of the tensile strength obtained by different heat treatment processes on very high cycle fatigue failure mechanisms.The material with higher tensile strength of 1 710 MPa exhibited typical gigacycle fatigue failure characteristics,whereas one with lower tensile strength of 1 010 MPa showed only traditional fatigue limit during the tests and no gigacycle failure could be found even when the specimen ran up to more than 10 8 cycles.Metallographic and fractographic analysis were carried out by an optical microscope (OM) and scanning electron microscope (SEM).It showed two different crack initiation mechanisms that for the specimen with lower tensile strength the crack prefers surface initiation and for that with higher strength the crack initiates from subsurface inclusions revealed by a fish-eye like microstructure.     

Parametric study on supersonic flutter of angle-ply laminated plates using shear deformable finite element method

The influence of fiber orientation,flow yaw angle and length-to-thickness ratio on flutter characteristics of angle-ply laminated plates in supersonic flow is studied by finite element approach.The structural model is established using the Reissner-Mindlin theory in which the transverse shear deformation is considered.The aerodynamic pressure is evaluated by the quasi-steady first-order piston theory.The equations of motion are formulated based on the principle of virtual work.With the harmonic motion assumption,the flutter boundary is determined by solving a series of complex eigenvalue problems.Numerical study shows that (1) The flutter dynamic pressure and the coalescence of flutter modes depend on fiber orientation,flow yaw angle and length-to-thickness ratio;(2) The laminated plate with all fibers aligned with the flow direction gives the highest flutter dynamic pressure,but a slight yawing of the flow from the fiber orientation results in a sharp decrease of the flutter dynamic pressure;(3) The angle-ply laminated plate with fiber orientation angle equal to flow yaw angle gives high flutter dynamic pressure,but not the maximum flutter dynamic pressure;(4) With the decrease of length-to-thickness ratio,an adverse effect due to mode transition on the flutter dynamic pressure is found.     

薄壁异形环截面管材料环向动态拉伸特性测试

针对薄壁异形环截面管状结构,结合有限元分析,提出了基于Hopkinson拉杆技术的环向材料动 态拉伸实验方法;设计了特殊的夹具,采用空心透射杆提高透射波幅值;并对1Cr18Ni9Ti材料薄壁异形环截 面管状结构进行不同应变率下的冲击拉伸实验。实验结果表明,该实验方法可适用于这种薄壁异形环截面管 状结构,该结构具有良好的塑性变形能力,断裂应变随应变率的提高明显降低,拉伸强度随应变率的提高明显 增大。     

玻纤增强复合材料高应变率拉伸实验研究

利用爆炸膨胀环实验技术,对玻璃纤维增强复合材料(GFRC)进行了高应变率(104s-1)下力学性能研究。实验中使用铜丝汽化引爆装药的方法对驱动环进行能量加载,并采用激光速度干涉仪(VISAR)测量试样环自由膨胀的质点速度,实现了玻璃纤维增强复合材料在104应变率下的一维拉伸破坏,并获取了该材料的速度时间曲线。经过计算得到了材料的应力应变关系,最后与该材料在准静态下、中高应变率下实验得到的数据进行了比较。