Research on the influences of confining pressure and strain rate on NEPE propellant: Experimental assessment and constitutive model

In order to study the influences of confining pressure and strain rate on the mechanical properties of the Nitrate Ester Plasticized Polyether (NEPE) propellant, uniaxial tensile tests were conducted using the self-made confining pressure system and material testing machine. The stress-strain responses of the NEPE propellant under different confining pressure conditions and strain rates were obtained and analyzed. The results show that confining pressure and strain rate have a remarkably influence on the mechanical responses of the NEPE propellant. As confining pressure increases (from 0 to 5.4 MPa), the maximum tensile stress and ultimate strain increase gradually. With the coupled effects of confining pressure and strain rate, the value of the maximum tensile stress and ultimate strain at 5.4 MPa and 0.0667 s⁻¹ is 2.03 times and 2.19 times of their values under 0 MPa and 0.00333 s⁻¹, respectively. Afterwards, the influence mechanism of confining pressure on the NEPE propellant was analyzed. Finally, based on the viscoelastic theory and continuous damage theory, a nonlinear constitutive model considering confining pressure and strain rate was developed. The damage was considered to be rate-dependent and pressure-dependent. The constitutive model was validated by comparing experimental data with predictions of the constitutive model. The whole maximum stress errors of the model predictions are lower than 4% and the corresponding strain errors are lower than 7%. The results show that confining pressure can suppress the damage initiation and evolution of the NEPE propellant and the nonlinear constitutive model can describe the mechanical responses of the NEPE propellant under various confining pressure conditions and strain rates. This research can lay a theoretical foundation for analyzing the structural integrity of propellant grain accurately under working pressure loading.     

Investigation on the process parameters of TIG-welded aluminum alloy through mechanical and microstructural characterization

Multi-pass TIG welding was conducted on plates (15×300×180 mm3) of aluminum alloy Al-5083 that usually serves as the component material in structural applications such as cryogenics and chemical processing industries. Porosity formation and solidification cracking are the most common defects when TIG welding Al-5083 alloy, which is sensitive to the welding heat input. In the experiment, the heat input was varied from 0.89 kJ/mm to 5 kJ/mm designed by the combination of welding torch travel speed and welding current. Tensile, micro-Vicker hardness and Charpy impact tests were executed to witness the impetus response of heat input on the mechanical properties of the joints. Radiographic inspection was performed to assess the joint's quality and welding defects. The results show that all the specimens displayed inferior mechanical properties as compared to the base alloy. It was established that porosity was progressively abridged by the increase of heat input. The results also clinched that the use of me-dium heat input (1-2 kJ/mm) offered the best mechanical properties by eradicating welding defects, in which only about 18.26% of strength was lost. The yield strength of all the welded specimens remained unaffected indicated no influence of heat input. Partially melted zone (PMZ) width also affected by heat input, which became widened with the increase of heat input. The grain size of PMZ was found to be coarser than the respective grain size in the fusion zone. Charpy impact testing revealed that the absorbed energy by low heat input specimen (welded at high speed) was greater than that of high heat input (welded at low speed) because of low porosity and the formation of equiaxed grains which induce better impact toughness. Cryogenic (-196 C) impact testing was also performed and the results corroborate that impact properties under the cryogenic environment revealed no appreciable change after welding at designated heat input. Finally, Macro and micro fractured surfaces of tensile and impact specimens were analyzed using Stereo and Scanning Electron Microscopy (SEM), which have supported the experimental findings.     

基于综合势力图的态势估计方法

在AI兵棋对抗中,能够更全面地理解态势信息是AI棋手获胜的前提条件.提出了基于综合势力图的态势估计方法,阐述了势力图的原理和一般生成过程,提出基于综合势力图的态势分析框架;将AI兵棋的静态信息、经验信息和动态信息计算叠加形成综合势力图,在此基础上分析敌方位置、视野以及火力威胁等态势相关信息,得到态势估计结果,为AI决策提供信息支撑;基于AI兵棋推演平台进行内置规则AI和基于势力图的AI之间的对抗实验,实验结果表明该方法能够提升AI决策的准确性,提高AI在兵棋对抗中的胜率.     

点火载荷下翼柱型装药结构完整性数值分析

针对固体火箭发动机翼柱型装药在点火载荷下结构完整性问题,提出了一种考虑三维损伤黏弹性本构性的数值模拟方法.基于商业有限元软件的二次开发平台,编写用户子程序,展开有限元数值计算,获取翼柱型装药在固化降温、点火载荷下装药结构的应力、应变与位移场分布.结果表明,在温度载荷与点火载荷下,药柱内表面变形模式是不同的.然而,不管在...     

基于广义随机Petri网GSPN的系统安全性研究

针对基于广义随机Petri网GSPN的动态系统安全性建模与分析方法进行了系统研究。基于Petri网、GSPN模型的基本原理,提出了关键状态搜索算法,并进行了安全性仿真分析.将广义随机Petri网的扩展模型应用于安全性分析领域,丰富了动态系统安全性问题的研究手段。     

火灾风险与保险调控初探

分析了国外保险与消防之间的相互关系和合作经验,简述了我国保险和消防存在合作的相互需要,探讨了运用保险调控火灾风险的措施。     

将军"斗胆直陈"与中央民主决策

实事求是是党的马克思主义思想路线的核心.这四个字说起来容易,做到却很难.它既受思想水平、认识能力的限制,同时又检验着一个人(特别是领导干部)的党性原则,所思所想所作所为是否真正出于公心.对中国革命作出了重大贡献的无产阶级革命家、军事家粟裕大将,堪称坚持实事求是的楷模.     

英语专业学生的中国文化失语症分析

语言与文化之间的密切关系使得英语国家文化成为英语教学的重要内容。而一些学者对部分大学生进行了使用英语转述中国特色文化话题的能力测试。结果表明,大多数受试者不能很好地用英语表达我们自己的民族文化,在可以接受的表述中还有较大部分为解释性意译。本文作者调查采用问卷形式,调查了英语专业各科英语教师50人,试图从英语专业教学的角度来分析造成英语专业中国文化失语现象的原因,并从教材、课程设置、教师能力、课外阅读等方面提出改进意见。     

空中突击兵力使用方案的优化方法

空中进攻战役全过程突击兵力使用方案的优化问题 ,是当前国内外亟待研究的重大课题。在提出多时段计划思想的基础上 ,给出了一种较为有效的优化模型 ,并探讨了有关的数据过滤问题     

基于HLA的C^4ISRK作战运用仿真系统探讨

C4ISRK是实现未来信息化战场"网络中心战"概念的一组必要的装备系统.着眼于为C4ISRK系统作战运用项目先期概念技术演示提供仿真平台,提出了C4ISRK系统的概念模型,在此基础上重点研究了基于HLA的C4ISRK作战运用仿真系统的总体框架及其设计,为该仿真系统的建立和仿真实施提供了技术支持.