Pull-in Instability Study of Carbon Nanotube Tweezers Under the Influence of Van der Waals Forces

The pull-in instability of two nanotubes under van der Waals force is studied. The cantilever beam with large deformation model is used. The influence of nanotube parameters such as the interior radius, the gap distance between the two nanotubes, etc, on the pull-in instability is studied. The critical nanotube length is determined for each specific set of nanotube parameters. The Galerkin method is applied to discretize the governing equations, and it shows good convergence.

压阻式高量程微加速度计的冲击校准

采用体硅微机械加工技术和扩散技术，制作压阻式高量程微加速度计，设计量程为50000 g_n。芯片材料为单晶硅，采用双列扁平陶瓷封装。为了测量其动态灵敏度，使用Hopkinson杆在约40000 g_n的加速度水平下进行了冲击校准。在电桥电压为6.33V的情况下，被测微加速度计的灵敏度为1.26 μV/g_n。

A new model for the energy release rate of fibre/matrix interfacial fracture

On the basis of the well-known shear-lag analysis of fibre/matrix interface stresses and the assumption of identical axial strains in the fibre and matrix, a new model for predicting the energy release rate of interfacial fracture of the fibre pull-out test model is attempted. The expressions for stresses in the fibre, matrix and interface are derived. The formula for interfacial debonding energy release rate is given. Numerical calculations are conducted and the results obtained are compared with those of the existing models.

井筒中钻井信息的传输动态分析

井眼轨道闭环控制校术是当今钻井技术领域的研究热点,而地面与井下的信息传输是这一高新技术中的重要环节。目前,地面与井下的无线信息传输系统主要是采用钻井液脉冲方式,如何提高传输深度和传输速率一直都是粘井液脉冲传输系统的研究主题。本文基于多相流理论,研究了粘井液脉冲信号的传输速度及其影响因素,分析了信号的动态传输特性和衰减规律。研究表明：脉冲信号在井筒中的往复传播类似于阻尼振荡；信号频率和钻井液粘度是影响信号衰减的主要可控因素。本文的研究对现有钻井液脉冲传输系统的改进具有参考价值。

含气体间隙装药撞击实验起爆模型

炸药装药发射安全性模拟实验表明，炮弹炸药装药底隙是诱发膛炸的最危险因素，证实“快速压缩间隙气体加热炸药”是炸药装药撞击起爆的最重要机制。本文分析炸药装药撞击起爆模拟实验，在忽略化学反应的条件下，建立了含气体间隙炸药装药撞击起爆一维模型，给出了描述低速气炮实验中气隙温度分布的方程及参数，即炸药最高温度的控制方程及参数。这些控制参数为气体的比热比、初始相对温度、气体压缩比、气体散热与输入功率比、界面传热系数比。

Dynamic properties and asymmetry of tension and compression of metal matrix composites under impact loading

The mechanical behaviors of 2124, Al-5Cu, Al-Li and 6061 alloys reinforced by silicon carbide particulates, together with 15%SiCw/6061 alloy, were studied under the quasi-static and impact loading conditions, using the split Hopkinson tension/compression bars and Instron universal testing machine. The effect of strain rate on the ultra tensile strength (UTS), the hardening modulus and the failure strain was investigated. At the same time, the SEM observations of dynamic fracture surfaces of various MMC materials showed some distinguished microstructures and patterns. Some new characteristics of asymmetry of mechanical behaviors of MMCs under tension and compression loading were also presented and explained in details, and they could be considered as marks to indicate, to some degree, the mechanism of controlling damage and failure of MMCs under impact loading. The development of new constitutive laws about MMCs under impact loading should benefit from these experimental results and theoretical analysis.

Effect of Particle Size on the Formation of Adiabatic Shear Band In Particle Reinforced Metal Matrix Composites

In this paper, the effect of particle size on the formation of adiabatic shear band in 2024 All matrix composites reinforced with 15% volume fraction of 3.5, 10 and 20 mum SiC particles was investigated by making use of split Hopkinson pressure bar (SHPB). The results have demonstrated that the onset of adiabatic shear banding in the composites strongly depends on the particle size and adiabatic shear banding is more readily observed in the composite reinforced with small particles than that in the composite with large particles. This size dependency phenomenon can be characterized by the strain gradient effect. Instability analysis reveals that high strain gradient is a strong driving force for the formation of adiabatic shear banding in particle reinforced metal matrix composites (MMCp).

七氟丁酸酐有序超薄膜的制备与结构

在涂敷有聚合物PEI涂层的单晶硅表面上制备了HFBA单层分子膜,接触角测量及XPS结果表明,HFBA在PEI表面产生了化学吸附发生了化学键合(酰胺键),形成了低表面能的HFBA单分子层膜.这一吸附反应的动力学行为可能表现为Langmuir单分子层化学吸附.

A Numerical Model of Rapid Solidification Processing of Ni-Al Alloy in Planar Flow Casting

A numerical model has been developed for simulating the rapid solidification processing (RSP) of Ni-Al alloy in order to predict the resultant phase composition semi-quantitatively during RSP. The present model couples the initial nucleation temperature evaluating method based on the time dependent nucleation theory, and solidified volume fraction calculation model based on the kinetics model of dendrite growth in undercooled melt. This model has been applied to predict the cooling curve and the volume fraction of solidified phases of Ni-Al alloy in planar flow casting. The numerical results agree with the experimental results semi-quantitatively.

Experimental Study on Dynamic Properties of High Strength Fiber Clusters

In this paper, the dynamic behaviors of several kinds of high strength fibers, including Kevlar, UHMPE, glass fibers, carbon fibers etc., are investigated experimentally, with a Split Hopkinson Tension Bar (SHTB). The effect of strain rate on the modulus, strength, failure strain and failure characteristics of fibers, under impact loading, is analyzed with the relative stress vs. strain curves. At the same time, the mechanism about the rate dependence of mechanical behaviors of various fibers is discussed based on the understanding on the microstructures and deformation models of materials. Some comments are also presented on the decentralization of experimental results, and a new method called traveling wave method is presented to increase the experimental accuracy. Research results obtained in this paper will benefit to understand the energy absorption and to build up the constitutive law of protective materials reinforced by high strength fibers.

压痕投影接触面积标定方法的研究

基于Oliver与Pharr方法的纳米压痕实验以其简单方便获得广泛的应用,但众多因素对压痕实验结果的影响范围并无明确的结论.其中压痕接触面积的确定是一个重要环节,该因素对实验结果,特别是小深度下的实验结果具有重要影响.仔细分析了Oliver与Pharr方法并进行了几种材料的纳米压痕实验,针对该方法在接触深度确定、不同深度范围下方法的适用性进行了说明.分析结果表明,对所有的材料使用统一的面积公式,只有在大压痕深度时才是适用的,而在小压痕深度时可能带来较大的误差.因此,应慎重使用由Oliver与Pharr方法得到的小压痕深度的硬度数据.

非理想界面对三相复合材料应力场的影响

对非理想界面的三相复合材料，提出了计算弹性应力场的微观力学模型，在适当的简化假设下，对带界相的颗粒增强和纤维增强复合材料，得到了应力场的计算公式。以剪切载荷为例给出了数值例子。给出的数值结果表明非理想界面对三相复合材料应力场的影响

Application of laser cladding technology to improve the interface of thermal barrier coatings

The present study is focused on improvement of the adhesion properties of the interface between plasma-sprayed coatings and substrates by laser cladding technology (LCT), Within the laser-clad layer there is a gradient distribution in chemical composition and mechanical properties that has been confirmed by SEM observation and microhardness measurement. The residual stress due to mismatches in thermal and mechanical properties between coatings and substrates can be markedly reduced and smoothed out. To examine the changes of microstructure and crack propagation in the coating and interface during loading, the three-point bending test has been carried out in SEM with a loading device. Analysis of the distribution of shear stress near the interface under loading has been made using the FEM code ANSYS, The experimental results show clearly that the interface adhesion can be improved with LCT pretreatment, and the capability of the interface to withstand the shear stress as well as to resist microcracking has been enhanced.