拉伸载荷作用下基体表层激光离散预处理对铬镀层／45钢基开裂行为的影响

采用激光离散预处理钢基体再电镀铬层技术得到了一种新型复合结构，研究了这种新型复合结构在拉伸载荷作用下的开裂行为特征，并与无激光处理钢基体的试样在同样试验条件下的开裂特征进行了对比分析。结果表明：有激光离散预处理钢基体试样的承载能力要高于无激光预处理钢基体试样的承载能力，且有激光处理的试样开裂区域在两个激光带之间（无激光处理区），主裂纹呈现明显的周期性特征。本研究结果可归结为激光预处理钢基体不仅改善了基体表层的应力状态和力学性能，而且还改善了后续铬镀层的力学性能。     

基于独立分量分析和神经网络的钢结构损伤识别方法

为了有效剔除钢结构振动信号中的噪声,提取用于损伤识别的特征量,采用独立分量分析方法分离统计独立信号,同时得到表征结构损伤状态的混合矩阵,然后将混合矩阵作为特征量输入至神经网络进行训练,最后将训练好的神经网络作为分类器进行结构损伤识别.在冲击载荷作用下,针对钢框架结构模型进行了不同损伤部位的振动实验,结果表明:基于独立分量分析和神经网络的损伤识别方法具有较高的识别率和可重复性,而且实现简单,在结构损伤识别领域具有较大的应用潜力.     

纳米SiO_2增韧改性环氧乙烯基酯树脂的性能研究

为了对环氧乙烯基酯树脂(EVER)进行增韧改性,采用KH570硅烷偶联剂对纳米SiO2进行表面处理,考察了纳米SiO2表面改性及其质量分数对EVER力学性能的影响。经过偶联剂处理的纳米SiO2复合材料在树脂基体中具备更好的分散性和相容性,力学性能明显优于纯EVER材料和未经偶联剂处理的复合材料。纳米SiO2质量分数为3%时,纳米SiO2复合材料的拉伸强度、断裂伸长率、冲击强度分别比纯EVER材料提高了42.10%,43.38%和91.91%;纳米SiO2质量分数为4%时,纳米SiO2复合材料的拉伸模量比纯EVER材料提高了34.57%。通过观察冲击断面的SEM照片,分析了纳米SiO2增韧改性的作用机理。结果表明:纳米SiO2增韧改性的关键在于诱发基体产生银纹,使其对裂纹扩展起到钝化、阻碍的作用。     

纳米颗粒和非晶相复合刷镀层n-Al2O3／Ni-P的制备

采用纳米电刷镀技术在钢基体表面制备了n-Al2O3/Ni-P复合刷镀层,研究了复合刷镀液中纳米颗粒含量、刷镀电压和刷镀笔移动速度对复合刷镀层中P和Al2O3含量的影响.优化后的工艺参数范围为刷镀液中n-Al2O3颗粒含量20～30 g/L、刷镀电压8～12 V、刷镀笔移动速度5～10 m/min.制备的n-Al2O3/Ni-P复合刷镀层组织致密,含有纳米颗粒和非晶相.     

高温空气下C/SiC复合材料力学性能测试

测试了C/SiC复合材料在高温空气下的压缩、弯曲和拉伸性能,利用扫描电子显微镜分析复合材料在室温与高温条件下的断口微观形貌。结果表明:从室温升温到1 000 ℃测试温度时,C/SiC复合材料的压缩强度由247 MPa降低至78 MPa,性能降低68%;弯曲强度由480 MPa降低至277 MPa,性能降低42%;拉伸强度由247 MPa降低至152 MPa,性能降低38%。高温氧化导致界面退化,损伤材料基体与碳纤维结构,加剧了纤维断裂程度,改变了纤维与基体的结合状态,纤维增韧机制逐渐消失,导致复合材料性能下降。     

小波分析在钢框架损伤识别中的应用研究

针对小波包能量谱损伤识别方法对结构激励源的依赖性,引入虚拟脉冲响应函数增强了小波包能量谱对激励的鲁棒性。为验证该方法对钢框架结构损伤识别的可行性和有效性,进行了3榀3跨钢框架3种工况下的模型对比试验,采用小波包能量谱损伤识别方法分析了不同实验工况下频响数据,识别结果符合损伤情况,验证了该方法的有效性。     

振动分析在钢桁架结构损伤预警中的应用

基于有限元分析软件ABAQUS平台,以一种钢桁架结构为例进行数值仿真分析;以白噪声信号作为环境激励信号,对钢桁架结构进行振动分析;结合虚拟脉冲响应函数和小波包能量谱分析法,对钢桁架结构在环境信号激励下进行损伤预警。最后,比较了不同测点的预警效果。结果表明:这两种方法的同时使用,对钢桁架结构在环境激励下进行损伤预警的效果十分明显,具有很好的工程应用价值。     

燃烧合成原位增韧氧化铝基复合陶瓷的显微结构与力学性能

通过燃烧合成技术制备出了氧化铝棒晶为基的Al2O3/ZrO2复合陶瓷棒材,研究了大体积Al2O3/ZrO2复合陶瓷的显微结构及力学性能.经对其性能测试发现,陶瓷的硬度和断裂韧性最高可达22.1 GPa和9.16 MPa·m0.5;通过对裂纹扩展路径观察,发现材料增韧是通过以氧化铝棒晶桥接与拔出增韧为主并伴有α-Al2O3片晶桥接多重增韧机制予以实现;经实验分析,可进一步认为以增大燃烧放热量来提高实际熔体温度,并在离心力作用下,进行材料高温高压合成,可显著提升材料的强韧性.     

CrTiAlN复合涂层的抗高温氧化性能与机理

采用多弧离子镀技术,利用Cr靶和TiAl靶,在活塞环材料65Mn钢基体上了制备CrTiAlN复合涂层,并对电镀Cr、CrN和CrTiAlN复合涂层在900℃下的高温氧化性能进行了比较,利用扫描电镜、能谱和X射线衍射观察和分析了样品表面氧化膜的性能,得到了CrTiAlN复合涂层的氧化机理。试验结果表明：CrTiAlN复合涂层在900℃时具有良好的抗高温氧化性能。     

共晶复合陶瓷损伤过程的有限元分析

针对共晶复合陶瓷的微观结构特征,建立了含强约束界面相的有限元模型,模拟了包含片状夹杂共晶复合陶瓷材料的外载应力场分布规律;应用ANSYS的APDL语言进行编程,对材料的损伤过程进行了研究。结果表明材料的破裂由基体损伤决定,随着外载荷的增加,损伤破坏沿界面延伸,并逐渐向基体内部扩展,最终造成基体的断裂。     

表面官能化对碳纳米管/环氧复合材料玻璃化转变温度及韧性的影响

通过碳纳米管的不同表面官能化,构造其与环氧树脂的不同界面。采用动态机械性能分析研究不同表面官能化碳纳米管对环氧树脂复合材料玻璃化转变温度的影响;采用摆锤冲击试验研究环氧树脂复合材料的韧性。结果表明:与纯环氧树脂相比,氨基化碳纳米管/环氧树脂复合材料的玻璃化转变温度升高,而羧基化碳纳米管/环氧树脂复合材料的玻璃化转变温度反而有所下降;碳纳米管/环氧树脂复合材料的冲击强度相比纯环氧树脂均提高了近一倍。复合材料性能的这些变化规律主要归因于不同表面官能化碳纳米管与环氧树脂基体间形成了不同的界面。     

Multifunctional A356 alloy/ PKSAnp composites: Microstructure and mechanical properties

Mechanical properties and microstructure of multifunctional composites produced with palm kernel shell ash nanoparticle (PKSAnp)-A356 alloy composites was studied. The composites were produced using Double layer feeding stir casting method (DLF-SCM) by adding 1 wt%‒4 wt.% PKSAnp. The microstructure, density, electrical and mechanical properties were determined. The results shows that there was a uniform distribution of the PKSAnp in A356 alloy. The mismatch at the interface between the PKSAnp and A356 alloy was 4.26%. Improvement of 30.47%, 41.91%, 49.52%, 40.90% and 65.09% were obtained for hardness values, tensile, yield strength, %elongation and impact energy at 4 wt% PKASnp. The work has established that the developed composites can be used for multifunctional applications where combination of toughness and strength is vital.     

添加SiC微粉对硅树脂先驱体转化3D Cf/Si-O-C材料性能的影响

以三维碳纤维织物和廉价的硅树脂为原料,采用先驱体转化工艺制备3D G/Si-O-C材料,考察了浸渍液中添加SiC填料对材料微观结构、力学性能和抗氧化性能影响.结果表明:添加适量的SiC填料有助于减少基体孔隙,改善界面结合,从而提高材料的力学性能;而SiC含量过高时,容易在材料内部形成闭孔,从而导致材料力学性能下降.当SiC微粉含量为18.2%时,材料具有最好的力学性能,弯曲强度和断裂韧度分别为421.3MPa和13.0 MPa·m1/2;而材料的抗氧化性能随着SiC微粉含量的增加而增加,当SiC微粉含量为25.0%时,材料的弯曲强度保留率最高,达到了89.5%.     

纳米Si-C-N粒子增强Si3N4 复合材料的结构与性能

本文用Ｓｉ－Ｃ－Ｎ纳米微粉做增强相,Ｓｉ３Ｎ４微粉为基相,采用热压的方法制备了ＳｉＣｐ／Ｓｉ３Ｎ４纳米复相陶瓷,所得的ＳｉＣｐ／Ｓｉ３Ｎ４复合材料的室温弯曲强度为８７８．５ＭＰａ,断裂韧性达１１．９６ＭＰａｍ１／２,同时应用扫描电镜（ＳＥＭ）、高分辨透射电镜（ＨＲＴＥＭ）对其结构进行了观察,讨论了结构与性能之间的关系。     

应用Isight的复合材料桁架结构优化设计

轻质复合材料及其结构以其优异的力学性能在航天航空飞行器上得到了广泛应用。考察玻璃纤维/环氧复合材料方形截面桁架在典型弯曲载荷工况条件下的非线性结构承载性能。采用Isight集成平台对桁架结构进行多参数优化设计,获得满足结构刚度和承载性能要求的最轻质桁架结构的几何参数,并分析最优化结构在载荷作用下的结构非线性响应行为。结果表明采用Isight平台对桁架结构进行多参数优化设计具有较高的效率和可信度。     

Simulation of natural fragmentation of rings cut from warheads

Natural fragmentation of warheads that detonates causes the casing of the warhead to split into various sized fragments through shear or radial fractures depending on the toughness,density,and grain size of the material.The best known formula for the prediction of the size distribution is the Mott formulae,which is further examined by Grady and Kipp by investigating more carefully the statistical most random way of portioning a given area into a number of entities.We examine the fragmentation behavior of radially expanding steel rings cut from a 25 mm warhead by using an in house smooth particle hydrodynamic(SPH) simulation code called REGULUS.Experimental results were compared with numerical results applying varying particle size and stochastic fracture strain.The numerically obtained number of fragments was consistent with experimental results.Increasing expansion velocity of the rings increases the number of fragments.Statistical variation of the material parameters influences the fragment characteristics,especially for low expansion velocities.A least square regression fit to the cumulative number of fragments by applying a generalized Mott distribution shows that the shape parameter is around 4 for the rings,which is in contrast to the Mott distribution with a shape parameter of 1/2.For initially polar distributed particles,we see signs of a bimodal cumulative fragment distribution.Adding statistical variation in material parameters of the fracture model causes the velocity numerical solutions to become less sensitive to changes in resolution for Cartesian distributed particles.     

基于仪器化压入技术的结构陶瓷材料断裂韧性测试

利用自主研制的仪器化压入仪,采用Vickers压头对氮化硅和氧化锆2种结构陶瓷进行了仪器化压入试验,通过压入载荷-深度曲线可识别材料的弹性模量E,通过测量压痕对角线直径可确定材料的维氏硬度HV,再通过测量压痕裂纹扩展长度即可得到材料的断裂韧性KIC,实现了在单一压入仪上基于Vickers压头对结构陶瓷材料断裂韧性的测试。与传统压痕法利用硬度计或纳米压入仪测试陶瓷材料断裂韧性相比,试验更简单快捷,可靠性高,同时测得信息量也更为丰富。试验测得2种结构陶瓷的断裂韧性分别为4.77～5.82 MPa.m1/2和7.22～8.94 MPa.m1/2。     

Effect of organo-modified montmorillonite nanoclay on mechanical,thermal and ablation behavior of carbon fiber/phenolic resin composites

The mechanical, thermal and ablation properties of carbon phenolic (C-Ph) composites (Type-I) rein-forced with different weight percentages of organo-modified montmorillonite (o-MMT) nanoclay have been studied experimentally. Ball milling was used to disperse different weight (wt) percentages (0, 1,2,4,6 wt.％) of nanoclay into phenolic resin. Viscosity changes to resin due to nanoclay was studied. On the other hand, nanoclay added phenolic matrix composites (Type-II) were prepared to study the dispersion of nanoclay in phenolic matrix by small angle X-ray scattering and thermal stability changes to the matrix by thermogravimetric analyser (TGA). This data was used to understand the mechanical, thermal and ablation properties of Type-I composites. Inter laminar shear strength (ILSS), flexural strength and flexural modulus of Type I composites increased by about 29％, 12％and 7％respectively at 2 wt.％ addition of nanoclay beyond which these properties decreased. This was attributed to reduced fiber volume fraction (％Vf) of Type-I composites due to nanoclay addition at such high loadings. Mass ablation rate of Type-I composites was evaluated using oxy acetylene torch test at low heat flux (125 W/cm2) and high heat flux levels (500 W/cm2). Mass ablation rates have increased at both flux levels marginally up to 2 wt.％ addition of nanoclay beyond which it has increased significantly. This is in contrast to increased thermal stability observed for Type-I and Type-Ⅱ composites up to 2 wt.％addition of nanoclay. Increased ablation rates due to nanoclay addition was attributed to higher insulation effi-ciency of nanolcay, which accumulates more heat energy in limited area behind the ablation front and self-propagating ablation mechanisms triggered by thermal decomposition of organic part of nanoclay.     

军事行政区主轴线空间节点秩序构建

结合营区规划实例,以军事行政区主轴线为研究对象,在分析现阶段军事行政区主轴线空间节点设计中比较集中存在的几个问题基础上,提出了构建军事行政区主轴线空间节点秩序及应遵循的一般原则,并以常见的入口区—广场区—办公区—训练区的轴线构成为例,对军事行政区主轴线各空间节点的秩序构建进行了空间、尺度及人性化等设计方法的探讨,为推动营区规划的正规化、现代化建设提供一些思路和方法。     

The salvo combat model with area fire

This article analyzes versions of the salvo model of missile combat where area fire is used by one or both sides in a battle. Although these models share some properties with the area fire Lanchester model and the aimed fire salvo model, they also display some interesting differences, especially over the course of several salvos. Although the relative size of each force is important with aimed fire, with area fire, it is the absolute size that matters. Similarly, although aimed fire exhibits square law behavior, area fire shows approximately linear behavior. When one side uses area fire and the other uses aimed fire, the model displays a mix of square and linear law behavior. © 2013 Wiley Periodicals, Inc. Naval Research Logistics 60: 652–660, 2013