复合芯材夹芯结构成型工艺研究

为了改善复合材料夹芯结构中芯材与面板界面结合强度,研制了一种新型夹芯结构,即复合材料柱/泡沫塑料复合芯材夹芯结构.该结构中用过渡层取代胶结层,使芯材和面板为一体,芯材由泡沫塑料和柱结构组成,其中柱结构是与面板同材质的纤维增强复合材料.通过该夹芯结构的芯材结构设计、加工工具的设计、加工工艺设计,使增强材料在法向上植入芯材中,并与上下面板的增强材料连通.由于在同一个工艺过程中固化成型,构成一个整体,没有界面,从根本上改善了面板与芯材之间粘接性能薄弱问题.试验结果表明,该结构具有较高的抗层间剪切、抗平压、抗剥离及抗疲劳性能.     

非连续边界层对圆柱声学共鸣频率的影响研究

基于声学一阶微扰理论,建立了低压下由于气 固界面的温度阶跃和速度滑移带来的边界层不连续性对圆柱声学共鸣频率的扰动规律,进一步发展了圆柱声学共振频率的非连续边界层修正模型,计算了非连续边界层对4种惰性气体、不同声学模式和不同压力及温度的影响。分析研究显示,气体处于低压状态时,温度阶跃和速度滑移会使声学共振频率发生偏移,不引入声能损耗。在50 kPa时,非连续边界层对声学共鸣频率的影响可达10×10^-6,表明非连续边界层修正项对于10^-6不确定度水平的尖端声学共鸣测量,是一个重要的不确定性来源。     

Blast resistance and energy absorption of foam-core cylindrical sandwich shells under external blast

The early time, through-thickness stress wave response of a foam-core, composite sandwich cylindrical shell under external blast is examined in this paper. Solutions for the transient response of the facesheets were derived as stress waves propagated through an elastic–plastic, crushable foam core. These solutions were found to be in good agreement with results from finite element analysis. The blast response of the composite sandwich cylindrical shell was shown to be affected by the magnitude and duration of the pressure pulse. High amplitude, low duration (impulsive) pressure pulses induced the greatest energy absorption. Low amplitude, long duration pressure pulses caused minimal energy absorption. The amount of energy absorbed increased and the failure load decreased with increasing core thickness. Sandwich shells with foams of varying density, compressive modulus and crushing resistance were also examined. The sandwich shells with the foam of the highest density, compressive modulus and crushing resistance (Divinycell HCP100) were found to be the most blast resistant to failure even though no energy was absorbed by them. Per unit weight, however, the shells with a lighter, less stiff and strong, Divinycell H200 foam core were more blast resistant to failure than shells with a Divinycell HCP100 foam core.     

Investigation of thermal stability of Mo thin-films as the buffer layer and various Cu metallization as interconnection materials for thin film transistor-liquid crystal display applications

Cu/Mo/Si multi-layer structures were fabricated to investigate diffusion behaviors and thermal stability between Cu and Mo. Physical vapor deposition (PVD), chemical vapor deposition, electroplating and electrolessplating were used to grow 100 nm thick Cu films as interconnection materials, and radio-frequency sputtering system was introduced to grow 37.5 nm thick Mo films as a buffer layer. All Cu/Mo/Si multi-layer specimens were annealed at 350 to 700 °C for 30 min. When the annealing temperature was over 600 °C, the Cu diffused through Mo into Si, and the Cu₃Si phase and Mo-Si intermetallic compounds formed at the Mo/Si interface. The diffusion mechanism is the grain boundary diffusion. The results indicate that Cu film deposited by PVD had best crystallinity, lower roughness, large adhesive energy and resistivity. The values of the resistivity, diffusion activity energy and large adhesive energy are 5.47 μΩ-cm, 0.948 eV and 2.46 N/m, respectively.     

Free vibration response of composite sandwich cylindrical shell with flexible core

This study deals with the free vibration analysis of composite sandwich cylindrical shell with a flexible core using a higher order sandwich panel theory. The formulation uses the classical shell theory for the face sheets and an elasticity theory for the core and includes derivation of the governing equations along with the appropriate boundary conditions. The model consists of a systematic approach for the analysis of sandwich shells with a flexible core, having high-order effects caused by the nonlinearity of the in-plane and the vertical displacements of the core. The behavior is presented in terms of internal resultants and displacements in the faces, peeling and shear stresses in the face–core interface and stress and displacement field in the core. The accuracy of the solution is examined by comparing the results obtained with the analytical and numerical results published in the literatures. The parametric study is also included to investigate the effect of geometrical properties such as radius of curvature, length and sector angle of the shell.     

水下夹芯复合空腔结构声学特性试验研究

引入空腔改善夹芯复合结构低频段吸声性能。建立了三种典型水下声隐身结构声学系统模型,在数值分析吸声性能影响因素基础上,运用脉冲声管试验方法,分析了空气背衬“硬”边界条件和水背衬“软”边界条件下,有无空腔试样、不同空腔间距、空腔形状和深度对谐振吸声峰值及峰值频率等的影响。试验结果表明,空腔显著改善了夹芯复合结构低频段吸声性能;空气背衬下,空腔间距越小,首阶谐振吸声峰值越大,峰值频率越低,水背衬条件下则相反;空腔体积越大,首阶谐振吸声峰值越小,峰值频率越低。     

碳／碳复合材料快速气相沉积工艺研究：——快速定向扩散法

设计出了一种碳／碳复合材料快速气相沉积新工艺，使得碳氢气体能借助于沉积室中的定向扩散装置并通过试样胚体厚度方向上的压力差快速定向扩散到试样胚体内部进行沉积。结果表明：沉积速度快，试样最终密度高而均匀。     

纤维增强树脂基复合材料环境加速老化性能研究

分析了复合材料湿热和热氧老化机理,对层合板复合材料及夹芯复合材料进行交变湿热和高低温加速环境试验,研究了材料的质量、弯曲性能等随老化环境、老化时间的变化情况。结果表明,复合材料具有良好的耐湿热和高低温环境稳定性,夹芯复合材料较层合板复合材料表现为更佳的性能稳定性。     

基于修正单层梁理论的夹层梁最大弯曲正应力计算

目的计算夹层梁横截面的最大弯曲正应力。方法将夹层梁等效成等截面均质单层梁,进而推导出了理论计算公式,并在此基础上进行了三点弯曲试验的算例研究。结果当破坏载荷与夹层梁横截面的尺寸一定时,随着芯层与总厚度比的增加,修正单层梁理论计算的最大正应力值逐渐增加,而单层梁理论计算的结果为恒定值。对于同样结构的夹层梁,随着芯层弹性模量与表层模量比的增加,修正单层梁理论计算的最大正应力与单层梁理论的差异值越来越小。结论修正单层梁理论与层合梁理论计算的结果是一致的,该方法可有效进行最大弯曲正应力的预测与计算。     

高性能功能梯度复合材料理论模型及力学行为分析

已有研究表明：通过使用沿厚度方向X型分布碳纳米管(CNTs)增强表面层,可有效提高复合材料夹芯结构抗屈曲能力。采用如此构型,将导致表面层刚度沿厚度方向突变,同时将使位移和应力发生骤变。因此,需要研究CNTs沿厚度方向分布构型对夹芯结构位移和应力的影响,目前鲜有高阶模型能准确分析此类问题。通过使用新型局部位移函数,该文构建了高性能功能梯度复合材料理论模型。基于此模型,给出了功能梯度复合材料夹芯梁弯曲的解析解,通过分析典型夹芯结构弯曲问题,并与三维有限元解对比验证了发展模型的性能。随后研究了CNTs沿厚度方向分布构型对夹芯结构位移和应力的影响。数值分析结果表明,发展的高性能理论模型能准确预测碳纳米管增强复合材料夹芯结构位移和应力的突变现象。     

夹芯复合材料阻尼性能的研究进展

随着航空航天轻质高速化和精密仪器设备自动化的发展,振动问题日益凸显.夹芯复合材料比强度高、比模量大、减振性能优良,兼具结构和功能一体化的特性,成为航空航天领域研究的热点.从复合材料基体、增强体、界面3个方面阐述了复合材料的减振机理,介绍了目前研究热门的夹芯结构以及芯材、面板、结合界面及其相互作用对阻尼性能的影响规律,概述了夹芯复合材料阻尼改性的研究现状,最后对夹芯复合材料阻尼的研究方向进行了展望.     

泡沫夹芯复合材料水声性能预测研究

针对泡沫夹芯复合材料声学测试的实际情况,建立了耦合声学有限元法的计算模型,针对计算模型进行了算例验证。结果表明,模型的预测值与试验值趋势吻合较好,计算方法是有效且可行的,可以用于预测泡沫夹芯复合材料的声学性能。同时,研究了与面板和芯材有关的四个参数对夹芯复合材料声学性能的影响规律。     

夹芯复合材料阻尼性能的研究进展

随着航空航天轻质高速化和精密仪器设备自动化的发展,振动问题日益凸显。夹芯复合材料比强度高、比模量大、减振性能优良,兼具结构和功能一体化的特性,成为航空航天领域研究的热点。从复合材料基体、增强体、界面3个方面阐述了复合材料的减振机理,介绍了目前研究热门的夹芯结构以及芯材、面板、结合界面及其相互作用对阻尼性能的影响规律,概述了夹芯复合材料阻尼改性的研究现状,最后对夹芯复合材料阻尼的研究方向进行了展望。     

复合材料夹芯结构准静态稳定性性能现状概述

复合材料夹芯结构由于其优异的比强度、比刚度及较小的表观密度的优点而广泛应用于航空航天、船舶等各个领域。本文从理论研究、仿真分析、实验研究这3个方面出发,综述了蜂窝、泡沫、点阵、褶皱4种夹芯结构在准静态稳定性研究方面的现状。蜂窝夹芯结构的研究较成熟,进一步的研究应集中于应用领域;泡沫夹芯结构在面芯问题方面有待增强,可考虑纤维缝合技术;褶皱夹芯结构理论方面有待进一步研究,潜力巨大;点阵夹芯结构较其他结构抗屈曲能力更强,但是依然存在面芯粘接问题。复合材料夹芯结构在准静态稳定性方面的问题主要集中在面芯粘接方面,纤维缝合技术可以有效增强面芯性能,该方面的研究对增强复合材料夹芯结构稳定性有较强的潜力。     

EMHD free-convection boundary-layer flow from a Riga-plate

The electro-magnetohydrodynamic (EMHD) free-convection flow of a weakly conducting fluid (e.g. seawater) from an electromagnetic actuator is considered. The actuator is a so called Riga-plate which consists of a spanwise aligned array of alternating electrodes and permanent magnets mounted on a plane surface. This array generates a surface-parallel Lorentz force which decreases exponentially in the direction normal to the (horizontal) plate. The free-convection boundary-layer flow induced by this body force is investigated numerically and analytically. It is shown that a certain length and velocity scale exists on which the flow characteristics are independent of the material properties of the fluid, as well as of the structural and functional parameters of the actuator. These universal velocity profiles are calculated numerically at different distances x from the leading edge and are discussed in some detail, both for the impermeable and the permeable Riga-plate when; in the latter case, a uniform lateral suction or injection of the fluid is applied. For the flow characteristics analytical approximations are reported. The asymptotic suction profiles approached for large values of x are given in exact analytical form. From a mathematical point of view the basic equations of the present boundary-value problem resemble those of the classical Blasius problem with an inhomogeneous forcing instead of an external flow and, accordingly, a homogeneous asymptotic condition.     

INTERLAMINAR SHEAR STRESS ANALYSIS OF COMPOSITE LAMINATE WITH LAYER REDUCTION TECHNIQUE

Interlaminar stress plays an important role in the delamination failure of laminated composites. A recently presented theory, the Interlaminar Shear Stress Continuity Theory (ISSCT), can directly and accurately predict interlaminar shear stresses in laminated composites by the constitutive equations. The present study further generalizes the derivation to a complete form from which many displacement-based laminate theories can be derived. Most of all, both the single-layer and multiple-layer approaches are incorporated into the analysis in the thickness direction. The laminate is discretized into several sublaminates and, then, a layerwise theory is applied in the analysis of this reduced laminate. This reduction in the number of layers used in the analysis makes the calculation of interlaminar shear stresses on the interested interface in a thick laminate more efficient. In addition, numerical solutions in closed-form and finite element form for laminates under cylindrical bending and bidirectional bending are examined. It is found that in the thickness direction the cubic order of the interpolation function and the discretization with four to six sublaminates can reduce the computational efforts dramatically and retain the accuracy of the predicted stresses within ±8 per cent.     

复合板材的超声特征扫描成像检测

介绍特征扫描(F-scan)超声成像检测技术,研制复合薄壁板材的特征扫描超声自动成像检测系统,通过此系统提取复合材料中缺陷的特征参数,对检测结果进行多种形式(B,C,F,相位特征)成像,在适当的判断条件下,实现缺陷的判断和识别.超声波层析图像表明:此设计实现层状复合材料层间粘结情况、层状材料中密度分布状态的分析和直观显示.     

夹芯复合材料基座结构设计与强度分析

提出了两型夹芯复合材料基座结构的设计方案,建立了夹芯复合材料基座数值分析模型,通过理论分析确定了影响基座结构刚度和强度性能的主要参数;应用有限元法。分析了铺层方式、支撑厚度和骨架形式等对直支撑基座结构刚度和强度性能的影响规律,计算并讨论了曲率半径对弧形支撑式基座刚度和强度性能的影响;比较了5种夹芯材料基座的结构力学性能,并通过优化设计,确定了夹芯复合材料基座结构形式。     

Effect of surface/interface on the dynamic stress of two interacting cylindrical nano-inhomogeneities under compressional waves

Based on the surface/interface elasticity theory, the effect of surface/interface on the dynamic stress of two interacting cylindrical nano-inhomogeneities under compressional waves is considered. The analytical solutions of displacement potentials are expressed by employing wave function expansion method and the expanded mode coefficients are determined by satisfying the boundary conditions at the interfaces. The addition theorem for cylindrical wave function is used to accomplish the superposition of wave fields in different coordinate systems. Analyses show that the effect of the interface properties on the dynamic stress is significantly related to the wave frequency of incident waves, the shear modulus ratio of the nano-inhomogeneities to matrix, and the relative position and distance between the two nano-inhomogeneities.     

复合材料夹层板的大挠度分析

本文构造一个复合材料夹层板矩形九节点单元,并应用于对称复合材料夹层板的大挠度分析,并讨论边界条件、夹心剪切模量以及而板和夹心厚度比对复合材料夹层极大挠度的影响,得到一些有意义的结论。