某型铜材料动态力学性能的数值模拟研究

采用一种高效的应力更新算法,运用Fortran语言编写Johnson—Cook本构模型的Vuamt子程序,模拟材料在高速冲击工况下的动态力学性能,研究塑性大应变、高应变率以及温度软化作用对材料力学性能的影响。     

便携式自寻的反坦克导弹攻顶弹道研究

便携式反坦克导弹在通过击顶方式打击目标时,要同时满足落角和精度的要求,以达到对目标的毁伤效能。首先推导带落角约束的最优比例导引律;然后设计携式反坦克导弹击顶弹道方案,导弹先出筒无控,以指数规律完成爬升,采用定攻角进行滑翔飞行,弹道末端运用推导的导引律来满足对落点和落角的约束。仿真结果表明,当反坦克导弹攻击不同距离的目标时,该弹道方案具有较强的有效性。     

大型舰艇箔条质心干扰防御反舰导弹仿真

箔条质心干扰是大型舰艇防御反舰导弹的重要手段。基于干扰机理分析,建立了以箔条云、舰艇切割效应模型为核心的干扰仿真模型,并利用仿真实例验证了该模型的正确性和合理性。在此基础上,通过典型场景下的仿真分析,揭示了大型舰艇箔条质心干扰运用的特殊性,为大型舰艇箔条质心干扰效果评估和运用方法研究提供模型支撑和定量依据。     

小波域非加性失真函数设计

在最小化嵌入失真隐写算法框架的基础上,提出了一种基于小波域的非加性失真函数图像隐写算法。首先在离散小波域设计了加性失真函数,主要考虑了亮度、频率和纹理掩蔽因子对载体失真的影响;然后结合模型矫正的方法对设计的加性失真函数进行了非加性矫正;最后结合网格码设计了隐写算法,将嵌入信息对载体的修改最小化,并且集中在人眼不敏感区域。实验结果显示,方案具有良好的视觉不可见性,且能抵抗空域SPAM特征隐写分析的攻击。     

In pursuit of accountability during and after war

ABSTRACT

This article aims to identify and elaborate the causes and ramifications of applying transitional justice, in particular accountability measures, to situations of war. It focuses on the correlations between peace and justice – and hence an important perspective on the question ‘how do wars end’. The article seeks to understand some of the main challenges associated with pursuing accountability for crimes committed in contemporary forms of conflict, including civil wars and abuses committed by major powers in armed conflict.     

多种服役环境下航空铝合金疲劳裂纹扩展行为

通过收集机场环境数据并依据环境谱编谱流程，编制出试验室环境下航空铝合金加速腐蚀试验谱，并依据该谱开展LD2CS铝合金预腐蚀疲劳试验。统计分析试验数据，利用影响平均值方法，筛选出三个重要腐蚀损伤表征量，即最大蚀坑深度、最大蚀坑宽度、点蚀率。通过归一化无量纲处理和加权平均方法，计算出腐蚀损伤综合指标α。对比不同损伤程度下预制裂纹疲劳扩展行为特点，定义腐蚀加速系数Ω(α)。利用加速腐蚀第18—20a的试验数据验证Ω(α)表达式的有效性，得到预测值相对误差均小于10%，这说明修正后的疲劳裂纹扩展公式适用于表示腐蚀损伤对长裂纹扩展的加速作用，为航空铝合金的损伤容限设计提供新的思路。     

地下工程非爆破开挖机械破碎法机理及应用

针对非爆破法开挖工序中的关键问题——导向孔布置方案优化,结合非爆破施工实作流程及工艺,利用波动理论探索了破碎锤冲击破岩机理。破碎锤通过钎杆冲击导向孔产生孔间贯穿裂缝进而破岩掘进,破碎锤冲击破岩的过程是岩石被拉坏的过程,孔间岩石中的切向应力是提高破岩效率的关键因素。基于岩石断裂力学理论,总结得出导向孔间裂缝产生、扩展、贯通的判据,并依托实际工程进行验算,理论计算结果与现场试验结果吻合良好,同时提出了导向孔布置优化方案的改进建议。     

增程修正弹单炮多发同时弹着火控技术研究

针对大口径火炮使用增程修正弹打远修近问题,建立了增程修正弹单炮多发同时弹着的控制算法,仿真验证了算法可在不同射程上实现单炮多发同时弹着,对发挥舰炮作战效能具有一定的意义。     

Fatigue crack propagation in a helicopter component subjected to impact damage

Damage tolerant methodology is increasingly used in aeronautical components,especially due the fact that the Aviation Regulation requires such an assessment in case an accidental damage occurs.At pre-sent,there is a strong and actual interest in applying such procedures to helicopter components that are subjected to high frequency cyclic loads.In this paper,an investigation on a damaged transmission shaft for a tail rotor transmission of an actual helicopter has been carried out focusing on the fatigue crack propagation.A complete sequence of experimental tests was performed in order to create an actual ballistic damage and to subsequently check the damage tolerant behaviour.The shaft was damaged by oblique ballistic impact and was subsequently subjected to torsional fatigue loading.During the fatigue cycles several cracks propagated from the ballistic damages.Both of these steps(impact and fatigue loading)were also simulated by a complex modelling approach based on Finite Element Models and fracture mechanics theory.The comparison between the experimental and numerical results shows a good agreement but it underlines the need for a very refined modelling technique capable to replicate all the features associated with the damage in order to reliably simulate the subsequent propagation phase.     

Hypersonic impact flash characteristics of a long-rod projectile collision with a thin plate target

Impact flash occurs when objects collide at supersonic speeds and can be used for real-time damage assessment when weapons rely on kinetic energy to destroy targets.However,the mechanism of impact flash remains unclear.A series of impact flash experiments of flat-head long-rod projectiles impacting thin target plates were performed with a two-stage light gas gun.The impact flash spectra for 6061 aluminum at 1.3-3.2 km/s collision speeds were recorded with a high-speed camera,a photoelectric sensor,and a time-resolved spectrometer.The intensity of the impact flash exhibited a pulse charac-teristic with time.The intensity(I)increased with impact velocity(V0)according to I∝Vn0,where n = 4.41 for V0 ＞ 2 km/s.However,for V0 ＜ 2 km/s,n = 2.21,and the intense flash duration is an order of magnitude less than that of higher V0.When V0 ＞ 2 km/s,a continuous spectrum(thermal radiation background)was observed and increased in intensity with V0.However,for V0 ＜ 2 km/s,only atomic line spectra were detected.There was no aluminum spectral lines for V0 ＜ 2 km/s,which indicated that it had not been vaporized.The initial intense flash was emission from excited and ionized ambient gases near the impact surface,and had little relationship with shock temperature rise,indicating a new mechanism of impact flash.