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.     

基于圆柱体缺陷构件的超声探伤重构研究

圆柱体构件中非轴对称人造缺陷偏心圆孔的超声探伤一直是无损检测的难点。基于脉冲反射原理设计超声实验平台,根据检测回波信号判定偏心圆孔缺陷所呈现的特征。在实验研究基础上,针对声场在圆柱体工件内部的传播情况,根据惠更斯原理以圆柱体为发射声源,基于k-wave仿真工具箱建立仿真平台,并利用声学传感器接收声波信号,设计的仿真平台能够实现360°同时刻采集工件的发射信号,同时利用传播过程中声压强弱的变化构建声场模型。根据采集的信号采用逆时反演重构模型,直观可视化地重构了内部缺陷的位置形状信息。     

基于BIST的3D SRAM中TSV开路测试算法研究与实现

基于3D-IC技术实现的3D SRAM,其电路中使用了大量的TSV。目前TSV制造工艺尚未成熟,使得TSV容易出现开路或短路故障,从而给3D SRAM的测试带来新的挑战。现有的2D BIST测试方式能够探测到3D SRAM中存在的故障,但并不能判定是TSV故障还是存储器本身故障；TSV专用测试电路虽然能够探测出TSV的故障,但需要特定的测试电路来实现,这就增加了额外的面积开销,同时加大了电路设计复杂度。基于此,本文提出了一种使用测试算法来探测TSV开路故障的方法,在不使用TSV专用测试电路且不增加额外面积开销的情况下通过BIST电路解决3D SRAM中TSV的开路故障检测问题。结果显示该TSV测试算法功能正确,能够准确探测到TSV的开路故障,并快速定位TSV的开路位置。     

Military spending and growth: a small open economy stochastic growth model

The paper analyzes the effects of military spending on economic growth in a small open stochastic endogenous growth model involving the supply-side and demand-side effects produced by military spending. We show that a rise in the military spending affects economic growth through four channels, including the crowding-out effect, the spin-off effect, the resource mobilization effect, and the portfolio effect. The net effect which depends on these four channels is ambiguous. Hence, we demonstrate that there exists an optimal defense burden that maximizes the economic growth rate.     

网络公开军事情报工作探析

随着信息技术的迅猛发展,互联网已深刻融入人们生产生活全过程,这使得网络中留下了各组织、机构和人员活动的海量信息痕迹。借助云计算、大数据等网络信息技术,这些信息痕迹已逐渐成为各国军事情报部门重要的情报来源,围绕网络空间展开的军事情报与反情报斗争日益激烈,需要引起高度重视。     

一种开放式PKI身份认证模型的研究

分析了传统PKI(Public Key Infrastructure)身份认证模型存在的问题,基于OCSP(Online Certificate Status Protocol)协议的证书状态验证服务和密钥验证服务相分离,造成了传统PKI身份认证模型的信任度下降,增加了身份认证的风险,跨CA(Certificate Authority)认证复杂度高,CA机构提供的身份认证服务不完整等问题。提出了一种开放式PKI身份认证模型,由CA中心独立完成两个验证服务,将OCSP应答机制改进为提供身份证明文件的方式,可有效解决上述问题。通过云信任评估模型对两种认证模型进行了量化评估,证明了本文提出的开放式身份认证模型可有效提高信任度。对该模型进行了原型实现,重点对性能问题进行了优化,实验测试表明,该模型具有实用价值。     

“心脏出血”漏洞的特点分析和对策建议

概括介绍＂心脏出血＂漏洞的基本概念、发现和公布、攻击和演变、处理和防范等有关情况,从安全通信协议软件、开源软件地位作用、开源软件代码管理和开源软件分析运用等方面分析特点并提出对策建议。     

预制缺陷柱壳结构的等效裂纹分析方法

针对传统有限元法在分析预制缺陷柱壳时出现的应力/应变计算精度不足、无法有效指导工程实践的问题,提出了一种具有高冗余度的等效裂纹分析方法。将预制缺陷视作典型裂纹,基于奇异裂纹元法对其进行裂纹稳定性分析,并根据稳定性分析结果来评估预制缺陷柱壳的结构完整性。通过该方法得到的分析结果具有比常规有限元分析更高的可靠性,对于导弹线式爆炸分离装置等工作环境恶劣、风险系数较高的预制缺陷柱壳结构而言,该方法有助于提升其设计的安全裕度,具有一定的工程实用性。     

快速传送语法的设计与实现

国际标准化组织提出的抽象语法ASN-1和传送语法ASN-BER功能强,通用灵活,但在一般实现中存在编码效率低和开销大的缺点。本文讨论提高编码效率和速度的一般方法,以及描述快速传送语法的设计与实现技术。     

Polynomial‐time approximation schemes for two‐machine open shop scheduling with nonavailability constraints

This paper addresses a two‐machine open shop scheduling problem, in which the machines are not continuously available for processing. The processing of an operation affected by a non‐availability interval can be interrupted and resumed later. The objective is to minimize the makespan. We present two polynomial‐time approximation schemes, one of which handles the problem with one non‐availability interval on each machine and the other for the problem with several non‐availability intervals on one of the machines. Problems with a more general structure of the non‐availability intervals are not approximable in polynomial time within a constant factor, unless . © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2006