Effect of post weld heat treatment on tensile properties and microstructure characteristics of friction stir welded armour grade AA7075-T651 aluminium alloy

This paper reports the effects of post weld heat treatments, namely artificial ageing and solution treatment followed by artificial ageing, on microstructure and mechanical properties of 12 mm thick friction stir welded joints of precipitation hardenable high strength armour grade AA7075-T651 aluminium alloy. The tensile properties, such as yield strength, tensile strength, elongation and notch tensile strength, are evaluated and correlated with the microhardness and microstructural features. The scanning electron microscope is used to characterie the fracture surfaces. The solution treatment followed by ageing heat treatment cycle is found to be marginally beneficial in improving the tensile properties of friction stir welds of AA7075-T651 aluminium alloy.     

未来指挥所发展展望

分析了国外尤其是美军在未来指挥所及其相关技术领域的研究与发展状况,指出未来指挥所将是未来军事指挥自动化系统发展的重要方向;通过介绍未来指挥所的基本概念、基本原理以及体系结构,引入并分析了未来指挥所系统将要涉及的主要关键技术;最后详细论证了未来指挥所系统的军事应用前景。     

The future challenges of NATO: An economic viewpoint

This article identifies and evaluates likely challenges facing NATO today and into the next millennium. These contingencies include ethnic‐based civil wars in Europe, transnational terrorism, rogue states, increased world income inequality, out‐of‐area conflicts, and environmental and resource security. Using concepts and tools from collective action, I assess these challenges and suggest effective policies for addressing them. NATO still has a crucial role to play in maintaining world security in the post‐Cold War era.     

An Empirical Analysis of the Arms Race Between South and North Korea

This study analyses an arms race between South and North Korea over the period 1963–2000. Despite the strategic importance of the Korean Peninsula, the arms race between South and North Korea has rarely been studied. In this study, the South–North arms race is empirically estimated using Richardson’s action–reaction model. The pattern of South–North arms race between the Cold War (1963–1989) and the post‐Cold War eras (1990–2000) as well as the existence of an arms race is examined comparing both countries’ defence spending, number of military personnel and tactical aircraft.     

Economic reconstruction amidst conflict: Insights from Afghanistan and Iraq

Economic reconstruction typically takes place after the end of war. Yet recently, economic reconstruction has been viewed as a means to ‘win hearts and minds’ during ongoing conflict. Drawing on a variety of reconstruction experiences from Afghanistan and Iraq, we identify four ‘reconstruction traps’ that result from the incentives and constraints faced by actors involved in economic reconstruction during ongoing conflict. These traps include: 1. the credible commitment trap, 2. the knowledge trap, 3. the political economy trap, and 4. the bureaucracy trap. Avoiding these traps is critical for successful economic reconstruction; and we discuss potential strategies for doing so.     

基于MRF模型和人工神经网络的遥感图像分类综合方法研究

本文总结了提高计算机遥感信息分类精度的四个有效途径，据此提出了基于三维Ｈｏｐｆｉｅｌｄ人工神经网络模型的遥感信息分类及平滑处理综合技术。实验表明，该方法可明显提高森林类型划分、土地利用调查等遥感应用专题的分类精度。     

‘A Time of War’: contextual and organisational dimensions in the construction of combat motivation in the IDF

This paper explores the construction of combat motivation in the Israel Defense Forces (IDF), arguing that although Israeli society at large is in a ‘Post Heroic’ era, the ‘Heroic Spirit’ is revealed during emergencies. A total of 1535 questionnaires were administered among combat soldiers during large-scale operations fought during national emergency and during small-scale routine operations. The results reveal differences in the construction of combat motivation typical for emergency vs. routine, as well as for reserves vs. regular units. These results indicate that the Post Heroic era is a condition that could be shifted according to cultural, organisational and individual determinants. This paper discusses the roots of these constructions and their implications on the theory of combat motivation and combat experience.     

Consequence of reinforced SiC particles and post process artificial ageing on microstructure and mechanical properties of friction stir processed AA7075

Friction stir processing and post process artificial ageing was successfully carried out on AA7075 with and without reinforcement of SiC particles producing defect free processed zone with uniform distribution of filler material. Effect of SiC particle reinforcement and artificial ageing times on the microstructural modifications was characterized using optical and electron microscopy, electron backscattered diffraction and X-Ray diffraction. Hardness, impact and wear tests were carried out to investigate mechanical behaviour before and after processing. Reinforcement of SiC particles during FSP and subsequent age hardening treatment brought about nearly twofold increase in hardness and impact toughness values by the combined effect of grain refinement, Zener pinning, dispersion strengthening and precipitation hardening. Significant improvement in wear resistance in terms of wear loss was also observed after processing compared to the reference material AA7075-T6. Fractured surface of post FSP age hardened AA7075 alloy exhibited features of ductile fracture during Charpy impact test.