3-SPR并联机构的隔振性能分析验证

对航天器或者雷达天线进行隔振是减少其受到振动载荷的有效方法.采用一种基于3-SPR并联机构的稳定平台进行主动隔振.建立上平台坐标系、下平台坐标系、全局坐标系,分析推导3个坐标系的姿态变换矩阵,将3-SPR并联机构作为稳定平台进行运动学和静力学特性分析,建立包含下平台和上平台同时运动的运动学公式及其静力平衡方程和静力传递...     

典型VDMOSFET单粒子效应及电离总剂量效应研究

利用252Cf源和60Coγ射线源对典型VDMOSFET进行单粒子效应和电离总剂量效应模拟试验,给出典型VDMOSFET的单粒子烧毁(SEB)、单粒子栅穿(SEGR)效应测量结果以及不同偏置条件下漏源击穿电压随辐照剂量的变化情况。结果表明,VDMOSFET对SEB和SEGR效应以及VDMOSFET漏源击穿电压对电离总剂量效应比较敏感,空间应用时需重点考虑VDMOSFET的抗SEB和SEGR能力;考核VDMOSFET的抗电离总剂量效应能力时对阈值电压和击穿电压等敏感参数应重点关注。     

Enhancement of forced convection heat transfer in a three-dimensional laminar channel flow with insertion of a moving block

Enhancement of heat transfer rate of a heat surface in a three-dimensional channel flow with insertion of a moving slender block is investigated numerically. A slender block is installed along the direction of the channel flow, and the movement of the slender block is in periodic motion and transverse to the channel flow. Due to the interaction between the channel flow and slender block moving, a large circulation vertical to the channel flow is induced and follows the moving slender block closely. The behaviors of the slender block and circulation destroy and suppress the velocity and thermal boundary layers on the heat surface periodically. These phenomena first observed cause the heat transfer rate of the heat surface to be enhanced especially in the downstream of the heat surface. The maximum magnitude of enhancement in this study is about 50%.     

Manufacturing and physical properties of all-polyamide composites

Based on the difference in melting points between polyamide 66 (PA66) fiber and polyamide 6 (PA6) matrix, all-polyamide composites were fabricated under various processing conditions. In these all-polyamide composites, the reinforcement and matrix share the same molecular structure unit (–CONH–(CH₂)₅–). Because of the chemical similarity of the two components, good bonding at the fiber/matrix interface could be expected. Effects of processing temperature and cooling rate on the structure and physical properties of composites were investigated by SEM, DMA, DSC analyses, and static tensile test. Fiber/matrix interface strength benefited from elevated processing temperature. The static tensile results showed that the maximum of tensile strength was observed in the processing temperature range of 225–245 °C. At different cooling rates, crystallization temperature of PA6 in the composites was increased compared to the pure PA6 because of the nucleation effect of PA66 fiber surface to the PA6 matrix. A study of the matrix microstructure in a single fiber-polymer composite gave proof of the transcrystalline growth at the fiber–matrix interface, the reason behind which was the similar chemical compositions and lattice structures between PA6 and PA66.     

In situ synthesis of bone‐like hydroxyapatite/polyamide 6 nanocomposites

BACKGROUND: Polymer/hydroxyapatite (HA) nanocomposites have emerged in recent years as a new class of biomaterials that can be used as artificial bone. Compared to pure HA or HA‐based bioceramics, and metallic implants, they exhibit good plasticity, improved toughness and good mechanical compatibility with natural bone. Compared to their microcomposite counterparts and the pristine polymer matrix, they show increased tensile strength and modulus, and enhanced bioactivity. RESULTS: In this study, polyamide 6 (PA6)/nanoscale HA (n‐HA) nanocomposites were prepared via in situ hydrolytic ring‐opening polymerization of ε‐caprolactam in the presence of newly synthesized n‐HA aqueous slurry. The synthesized n‐HA, which is similar to bone apatite in chemical composition, microscopic morphology and phase composition, dispersed uniformly in the composites even if its loading was up to 60 wt%. The PA6/n‐HA composites show a similarity to natural bone in chemical composition to a certain extent. Mechanical tests show that the composites are reinforced considerably by the incorporation of needle‐like n‐HA, and the composites have mechanical properties near to those of natural bone. CONCLUSION: The PA6/n‐HA nanocomposite with high n‐HA content shows a similarity to natural bone in terms of chemistry and mechanical properties. This makes it a possible candidate for biomaterials suitable for bone repair or fixation. Copyright © 2008 Society of Chemical Industry     

Effects of shell thickness of polystyrene‐encapsulated Mg(OH)2 on flammability and rheological properties of high‐impact polystyrene composites

Polystyrene (PS)‐encapsulated magnesium hydroxide (Mg(OH)₂) particles with various shell thicknesses were successfully prepared using a method of in situ polymerization of styrene in a high‐speed mixer. High‐impact polystyrene (HIPS)/Mg(OH)₂ composites were prepared by melt blending. They were characterized using cone calorimetry, horizontal burning rate, rheology and scanning electron microscopy in order to investigate the effects of the shell thickness of the PS‐encapsulated Mg(OH)₂ on the flame retardancy and rheological properties of the resulting composites. Rheological tests showed that the composites containing encapsulated Mg(OH)₂ had a stronger solid‐like response at low frequency than that of the sample containing untreated Mg(OH)₂. However, with PS/Mg(OH)₂ ratio increasing up to 6.0 wt% and above, the dynamic viscosity, loss modulus and storage modulus of HIPS/Mg(OH)₂ composites decreased. The optimum PS/Mg(OH)₂ ratio, 4.5 wt%, was determined using a new ‘crossover point’ rheological method. The combustion tests showed that compared to the composites containing untreated Mg(OH)₂, the fire retardancy of the composites containing PS‐encapsulated Mg(OH)₂ was improved significantly. Also, there appeared to be a critical PS/Mg(OH)₂ ratio, namely 6.0 wt%, for optimum flame‐retarding properties. However with the continuous increase of PS/Mg(OH)₂ ratio, the fire resistance of the composites declined somewhat, which can be explained by acceleration of combustion of the composites due to the introduction of free PS chains of low molecular weight on the surface of Mg(OH)₂. Copyright © 2007 Society of Chemical Industry     

纳米量子点能级以及能隙计算和修正

用一个简单模型分析了量子点产生能级的原因,推导出能级与量子点尺寸的表达式。根据量子点表面势垒为有限值的特点以及表面存在衰减波,提出量子点内电子波函数不完全满足驻波条件的观点,在量子点的能级表达式中引入一个修正系数。结合量子点表面衰减波的特征,给出量子点修正系数的计算方法。通过理论计算表明：量子点的能级以及能级之间的能量差（间隙）不但与量子点的尺寸有关,而且与其边界条件有关。特别是对于非光滑的表面,其表面势垒对量子点的能级与能隙影响非常大。     

含预埋梁蜂窝夹层结构数值仿真与试验研究

含预埋梁蜂窝夹层结构是在纯蜂窝结构基础上改进得到的全新结构形式,综合了蜂窝结构和桁条铆接结构的优点,但该类结构的载荷分布形式以及失效模式缺乏相关研究。针对上述问题,结合国内在研尺寸最大的含预埋梁铝蜂窝夹层结构,采用层合板加筋方法进行了数值仿真,设计全尺寸物理试验对结构性能进行了试验验证。通过数值仿真和试验对比,验证了层合板加筋方法模拟含预埋梁蜂窝结构的准确性,同时研究了该类结构的载荷分布和失效模式,并为同类结构设计提供了参考依据。     

DDS体系在飞行器地面测试系统中的应用

针对飞行器地面测试系统需要满足多种不同类型的数据传输、较高的数据传输速率、较高的数据传输实时性的目的,采用广播式网络通信体系DDS数据通信体系进行飞行器地面测试系统构建的方法。通过某型号飞行器地面测试以及各项大型试验。得出DDS数据通信体系具有高实时性、系统网络架构易于扩展、能够适应不同类型数据传输、数据通信模式灵活可配置等诸多结论,DDS数据通信体系完全能够满足飞行器地面测试的应用需求。     

Radiation damage induced by 2 MeV protons in CdTe and CdZnTe semiconductor detectors

An experimental investigation of the radiation damage induced on CdTe and CdZnTe semiconductor detectors has been performed by exposing a set of samples to increasing doses of 2 MeV protons produced by a 1.7 MV Tandetron accelerator.The modifications in the detector performances have been studied through the dark current measurements and spectroscopic response analyses at low and medium energies. The deep levels of the materials have been investigated by means of Photo Induced Current Transient Spectroscopy analyses. The evolution of some important parameters (energy resolution, charge collection efficiency, leakage current, activation energies and capture cross-section of deep level defects) have been monitored with respect to increasing proton exposures and the results obtained give us some important indications on the modifications of the material properties as well as on the performances degradation of the detectors.