Yasir Mahmood  Peng-wan Chen  I.A.Bataev  Xin Gao 《防务技术》2021,17(5):1592-1601

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.  相似文献   

    

Sigrún Andradóttir  Andrei A. Prudius 《海军后勤学研究》2010,57(6):583-604

We present, analyze, and compare three random search methods for solving stochastic optimization problems with uncountable feasible regions. Our adaptive search with resampling (ASR) approach is a framework for designing provably convergent algorithms that are adaptive and may consequently involve local search. The deterministic and stochastic shrinking ball (DSB and SSB) approaches are also convergent, but they are based on pure random search with the only difference being the estimator of the optimal solution [the DSB method was originally proposed and analyzed by Baumert and Smith]. The three methods use different techniques to reduce the effects of noise in the estimated objective function values. Our ASR method achieves this goal through resampling of already sampled points, whereas the DSB and SSB approaches address it by averaging observations in balls that shrink with time. We present conditions under which the three methods are convergent, both in probability and almost surely, and provide a limited computational study aimed at comparing the methods. Although further investigation is needed, our numerical results suggest that the ASR approach is promising, especially for difficult problems where the probability of identifying good solutions using pure random search is small. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010  相似文献   

    

Haitao Liao  Elsayed A. Elsayed 《海军后勤学研究》2010,57(5):472-488

Accelerated life testing (ALT) is widely used to determine the failure time distribution of a product and the associated life‐stress relationship in order to predict the product's reliability under normal operating conditions. Many types of stress loadings such as constant‐stress, step‐stress and cyclic‐stress can be utilized when conducting ALT. Extensive research has been conducted on the analysis of ALT data obtained under a specified stress loading. However, the equivalency of ALT experiments involving different stress loadings has not been investigated. In this article, a log‐location‐scale distribution under Type I censoring is considered in planning ALT. An idea is provided for the equivalency of various ALT plans involving different stress loadings. Based on this idea, general equivalent ALT plans and some special types of equivalent ALT plans are explored. For demonstration, a constant‐stress ALT and a ramp‐stress ALT for miniature lamps are presented and their equivalency is investigated. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010  相似文献   

Poppy Blues: The Collapse of Poppy Eradication and the Road Ahead in Afghanistan     

James A. Nathan 《Defense & Security Analysis》2009,25(4):331-353

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The nature of military culture     

R. A. D. Applegate RA  J. R. Moore 《Defense & Security Analysis》1990,6(3):302-305

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Recent titles dealing with Indian and Nepali Maoists     

Thomas A. Marks 《Small Wars & Insurgencies》2014,25(2):487-491

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Ross A. Kennedy 《战略研究杂志》2013,36(7):1058-1070

The books under review here, by Robert F. Hannigan, John A. Thompson, Trygve Throntveit, and Adam Tooze, offer an interpretation of Wilsonian internationalism and what happened to it in the 1920s. For Tooze and Hannigan, Wilsonianism was primarily a project to attain American predominance in the world. For Throntveit, Wilsonian internationalism constituted a pragmatic yet radical effort to end competitive power politics. Thompson disagrees with these arguments and asserts that the key to understanding US policy lay in how US leaders conceptualized American power. Thompson’s interpretation is especially compelling in explaining why the United States failed to engage itself more assertively in international affairs in the 1920s – a failure Tooze suggests undermined the viability of the postwar international system.  相似文献   

    

Nicholas A Lambert 《战略研究杂志》2013,36(2):272-297

The Fisher naval revolution of 1904–10 represented a deliberate attempt to achieve defense transformation to bolster Britain's pretensions to global naval supremacy. The vision called for smaller, more capable forces to do the work of larger, more expensive conventional formations. It consisted of three main elements. First, the replacement of the traditional station fleet system for protecting overseas interests by rapid deployment forces comprised of battlecruisers that could be ‘maneuvered’ by wireless to combat specific enemy threats. Second, at home, instead of a sea control strategy based upon a superior battle-fleet, a sea denial strategy based on flotilla defense commanded and controlled from London via wireless. The third element of the Fisher revolution depended upon ‘plunging’, or shaping and directing technological change through a special relationship with armaments firms. A sophisticated information-communications network was integral to the revolution.  相似文献   

    

Niel A. Smith  Nathan W. Toronto 《Small Wars & Insurgencies》2013,24(3):519-528

A recent article, ‘Rage Against the Machines’, does a disservice to the debate over what explains counterinsurgency (COIN) success. While it establishes a negative correlation between the diffusion of military mechanization in the state system and COIN success, its theoretical argument does not hold up under close scrutiny and its micro-case comparison of two units in Iraq during 2003–2004 ignores obvious counter-examples and factors that influence COIN success, such as leadership. A deeper inquiry would have revealed that there is much more to COIN success than simply not having access to vehicles.  相似文献   

    

David A. Patten 《Small Wars & Insurgencies》2013,24(5):879-906

Taking insurgency sponsorship as an instrument states have available for achieving foreign policy objectives, I consider how state-sponsors could best manipulate their support to maximize control of the proxy group. Building on research that models the state-sponsor–insurgent relationship using a principal–agent framework, I identify two key vulnerabilities to which the state-sponsor is exposed: adverse selection and agency slack. As an original contribution to the literature on state-sponsorship of insurgency, I articulate reasons why certain forms of support would be most conducive to overcoming these problems and illustrate how South Africa and Iran used those kinds of support to influence the behavior of their proxies, RENAMO and Hezbollah. Additionally, I consider how this principal–agent analysis of insurgency sponsorship also could apply when the principal is an international terrorist organization such as al Qaeda. Finally, I address the relevance of these ideas to two contemporary conflicts taking place in Syria and the Congo.  相似文献