AMESim与MATLAB/Simulink联合仿真技术及应用

分析了AMESim与MATLAB/Simulink的特点,对两者的联合仿真技术进行了研究,解决了联合仿真的接口问题.并把该技术应用于主动悬架系统,取得了良好效果.     

WSEIAC模型的中远程空空导弹武器系统效能分析

依据中远程空空导弹武器平台系统的战术指标,建立了中远程空空导弹武器平台系统的效能评价体系.对ADC扩展模型中的人为因素K进行了修正,在能力矩阵C中增加对载机生存能力和信息支持能力的体现.在此基础上给出了修正扩展模型下的系统效能,计算了在原始ADC模型下的系统效能,并对两种模型下的效能差异进行了比较.     

军用飞机综合效能/费用评估方法

军用飞机的效能与费用是两个相互制约的因素,对两者进行科学合理的综合评估,对于军用飞机的发展和使用有着很重要的意义。在分析综合效能/费用的基本评估指标基础上,提出了在军用飞机全寿命周期综合效能/费用评估指标,重点对作战使用阶段的最佳效能/费用进行评估分析,最后给出结论。     

The effect of al particle size on thermal decomposition,mechanical strength and sensitivity of Al/ZrH2/PTFE composite

To study the thermal decomposition of Al/ZrH2/PTFE with different Al particle size as well as mechanical strength and impact sensitivity under medium and low strain rates, molding-vacuum sintering was adopted to prepare four groups of power materials and cylindrical specimens with different Al particle size. The active decomposition temperature of ZrH2 was obtained by TG-DSC, and the quasi-static me-chanics/reaction characteristics as well as the impact sensitivity of the specimen were studied respec-tively by quasi-static compression and drop-hammer test. The results show that the yield strength of the material decreased with the increase of the Al particle size, while the compressive strength, failure strain and toughness increased first and then decreased, which reached the maximum values of 116.61 MPa, 191％, and 119.9 MJ/m respectively when the Al particle size is 12—14μm because of particle size grading. The specimens with the highest strength and toughness formed circumferential open cracks and reacted partly when pressed. Those with developmental cracks formed inside did not react. It is considered that fracture of specimens first triggered initial reaction between Al and PTFE to release an amount of heat. Then ZrH2 was activated and decomposed, and participated in subsequent reaction to generate ZrC. The impact sensitivity of the specimens decreased with the increase of Al particle size.     

Micromechanical simulation and experimental investigation of aluminum-based nanocomposites

Ceramic reinforced metal matrix nanocomposites are widely used in aerospace and auto industries due to their enhanced mechanical and physical properties. In this research, we investigate the mechanical properties of aluminum/Nano-silica composites through experiments and simulations. Aluminum/Nano-silica composite samples with different weight percentages of silica nanoparticles are prepared via powder metallurgy. In this method, Nano-silica and aluminum powders are mixed and compressed in a mold, followed by sintering at high temperatures. Uniaxial tensile testing of the nanocomposite samples shows that adding one percent of Nano-silica causes a considerable increase in mechanical properties of nanocomposite compared to pure aluminum. A computational micromechanical model, based on a representative volume element of aluminum/silica nanocomposite, is developed in a commercial finite element software. The model employs an elastoplastic material model along with a ductile damage model for aluminum matrix and linear elastic model for nano-silica particles. Via careful determination of model parameters from the experimental results of pure aluminum samples prepared by powder metallurgy, the proposed computational model has shown satisfactory agreement with experiments. The validated computational model can be used to perform a parametric study to optimize the micro-structure of nanocomposite for enhanced mechanical properties.     

Effect of functionally-graded interphase on the elasto-plastic behavior of nylon-6/clay nanocomposites; a numerical study

In nanocomposites, the interphase thickness may be comparable to the size of nano-particles, and hence, the effect of interphase layers on the mechanical properties of nanocomposites may be substantial. The interphase thickness to the nano-particle size ratio and properties variability across the interphase thickness are the most important affecting parameters on the overall behavior of nanocomposites. In this study, the effect of properties variability across the interphase thickness on the overall elastic and elasto-plastic properties of a polymeric clay nanocomposite (PCN) using a functionally graded (FG) interphase is investigated in detail. The results of the computational homogenization on the mesoscopic level show that Young's modulus variation of the interphase has a significant effect on the overall elastic response of nanocomposites in a higher clay weight ratio (Wt). Moreover, strength variation through the interphase has a notable effect on the elasto-plastic properties of PCNs. Also, the increase or decrease in stiffness of interphase from clay to matrix and vice versa have a similar effect in the overall behavior of nanocomposites.     

Experimental and numerical investigations of interface properties of Ti6Al4V/CP-Ti/Copper composite plate prepared by explosive welding

Explosive welding technique is widely used in many industries. This technique is useful to weld different kinds of metal alloys that are not easily welded by any other welding methods. Interlayer plays an important role to improve the welding quality and control energy loss during the collision process. In this paper, the Ti6Al4V plate was welded with a copper plate in the presence of a commercially pure titanium interlayer. Microstructure details of welded composite plate were observed through optical and scanning electron microscope. Interlayer-base plate interface morphology showed a wavy structure with solid melted regions inside the vortices. Moreover, the energy dispersive spectroscopy analysis in the interlayer-base interface reveals that there are some identified regions of different kinds of chemical equilibrium phases of Cu–Ti, i.e. CuTi, Cu₂Ti, CuTi₂, Cu₄Ti, etc. To study the mechanical properties of composite plates, mechanical tests were conducted, including the tensile test, bending test, shear test and Vickers hardness test. Numerical simulation of explosive welding process was performed with coupled Smooth Particle Hydrodynamic method, Euler and Arbitrary Lagrangian-Eulerian method. The multi-physics process of explosive welding, including detonation, jetting and interface morphology, was observed with simulation. Moreover, simulated plastic strain, temperature and pressure profiles were analysed to understand the welding conditions. Simulated results show that the interlayer base plate interface was created due to the high plastic deformation and localized melting of the parent plates. At the collision point, both alloys behave like fluids, resulting in the formation of a wavy morphology with vortices, which is in good agreement with the experimental results.     

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。     

The ballot or the bomb belt: the roots of female suicide terrorism before and after 9/11

ABSTRACT

In recent years, an upward trend in terrorist attacks has mirrored an increase in suicide attacks. According to our preliminary analysis, the events of September 11^th marked a sea change in the number of terrorist attacks. While a rich literature has evaluated why terrorists participate in suicide attacks, none have considered the uptick in volume after 9/11, and fewer yet have considered how female fighters may be contributing to this. We evaluate how both structural and female-specific factors affect the likelihood of female fighter suicide attacks. Recent literature discovered a trend in terrorist groups using females as suicide bombers due to cultural norms that permit them to get closer to targets. We test our theory using data from the Chicago Project on Security and Threats Suicide Attack Database (CPOST-SAD) and various datasets from the Quality of Government (QOG) compendium for the 1986–2016 time period. We construct a series of models that consider both female-specific and structural factors that could explain variation in the number of female suicide attacks. Our results indicate that our models encompass relatively stable patterns. Female political empowerment, female educational attainment, and female employment rates are significant and positive in our post-9/11 models, indicating that they may increase female suicide attacks. Democracy is a relevant structural factor and generally yields a positive effect on female suicide attacks across both time periods and multiple models. Ethnic fractionalization is significant in both time periods but yields a negative effect before 9/11 and a positive effect in the later period.