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171.
Effects of annealing temperature on the microstructure and properties of the 25Mn-3Si-3Al TWIP steel 总被引:3,自引:0,他引:3
Microstructures and mechanical properties of the 25Mn twinning induced plasticity (TWIP) steel at different annealing temperatures were investigated. The results indicated that when the annealing temperature was 1000°C,the 25Mn steel showed ex-cellent comprehensive mechanical properties,the tensile strength was about 640 MPa,the yield strength was higher than 255 MPa,and the elongation was above 82%. The microstructure was analyzed by optical microscopy (OM),X-ray diffraction (XRD),and transmission electron... 相似文献
172.
Surface performance of workpieces processed by electrical discharge machining in gas 总被引:1,自引:0,他引:1
The surface performance of workpieces processed by electrical discharge machining in gas(dry EDM)was studied in this paper.Firstly,the composition,micro hardness and recast layer of electrical discharge machined(EDMed)surface of 45 carbon steels in air were investigated through different test analysis methods.The results show that the workpiece surface EDMed in air contains a certain quantity of oxide,and oxidation occurs on the workpiece surface.Compared with the surface of workpieces processed in kerosene,fewer cracks exist on the dry EDMed workpiece surface,and the surface recast layer is thinner than that obtained by conventional EDM.The micro hardness of workpieces machined by dry EDM method is lower than that machined in kerosene,and higher than that of the matrix.In addition,experiments were conducted on the surface wear resistance of workpieces processed in air and kerosene using copper electrode and titanium alloy electrode.The results indicate that the surface wear resistance of workpieces processed in air can be improved,and it is related with tool material and dielectric. 相似文献
173.
传统的网络安全措施,如加密认证、防火墙和入侵检测系统等,虽然在保护信息的保密性、完整性、可用性和控制访问方面有一定的效果,但在协同和预警方面依然存在不足.文章提出了1个基于multi-agents的网络安全防卫系统,该系统由协同预警定位系统、协同审计系统、安全隔离系统、事故恢复系统等多个模块构成,模块之间由多个多级分层agents来负责通信任务.系统控制中心的agent server负责控制和协调整个安全体系,制定全网统一的安全控制策略.在该系统中,整个网络被划分成不同级别的分区,建立不同级别的协同预警定位系统,各分区既相互协作,又能够独立自治,通过协作的方式共同维护着整个网络的安全.在IPv6环境下测试的结果表明,该系统可以高效进行预警,IDS的捕获率约为95%、漏报率小于6%、误报率小于7%. 相似文献
174.
基于三维模型的飞机红外图像仿真研究 总被引:1,自引:0,他引:1
要对红外成像制导导弹攻击飞机的过程进行仿真,需要生成目标飞机的红外图像。当飞机受到导弹攻击时会采取各种机动动作进行规避,这就使导引头所探测到的图像随着弹目距离、飞机姿态而变化,所生成的红外图像必需能够反应这种变化。文章首先根据能量守恒定律和黑体辐射定律,并综合考虑了大气透过率、光学系统透过率和探测器响应率的影响,推导了导引头探测器接收到的飞机红外辐射功率计算公式,利用该公式计算出所建飞机三维模型每个面的辐射功率,并将其转换为红外灰度值,最后利用OpenGL技术直接对飞机三维模型进行操作,以实现各种位置、姿态下三维飞机模型到二维图像的转换,并用光学系统的点扩散函数与输出的图像进行卷积,最终得到反映光学模糊的飞机红外图像,最后开发了红外图像仿真软件,利用该软件生成了几种不同位置、不同姿态下的飞机红外图像,并对其进行了分析。 相似文献
175.
176.
大型复杂工程结构的损伤实际上是一个渐进损伤的过程,为解决结构损伤识别中非平稳随机信号的时变性并有效地识别这个损伤过程,研究了基于Hilbert-Huang变换的结构渐进损伤特征提取方法.首先模拟产生了多自由度结构系统发生渐进损伤的加速度振动信号;然后对加速度振动信号进行经验模式分解,将其分解为多个平稳的固有模式函数之和;再选取若干个包含主要损伤信息的固有模式函数进行Hilbert变换,提取瞬时频率作为特征参数进行损伤特征提取.研究结果表明:HHT是一种有效的信号处理方法,通过提取瞬时频率,可以准确地提取结构渐进损伤的特征. 相似文献
177.
On the numerical simulation of active scalar, a new explicit algebraic expression on active scalar flux was derived based
on Wikstr?m, Wallin and Johansson model (a
WWJ
model). Reynolds stress algebraic expressions were added by a term to account for the buoyancy effect. The new explicit Reynolds
stress and active scalar flux model was then established. Governing equations of this model were solved by finite volume method
with unstructured grids. The thermal shear stratified cylinder wake flow was computed by this new model. The computational
results are in good agreement with laboratorial measurements. This work is the development on modeling of explicit algebraic
Reynolds stress and scalar flux, and is also a further modification of the a
WWJ
model for complex situations such as a shear stratified flow.
Supported by the National Nature Science Foundation of China (Grant Nos. 50679019, 50009001), the National Basic Research
Program of China (“973” Project) (Grant No. 2008CB418202), the Project of “Six Talent Peak” of Jiangsu Province (08-C), Social
Technology Development Foundation of Jiangsu Province (Grant No. BS2006095) and the “908” Special Foundation of Jiangsu Province
(Grant No. JS-908-02-06) 相似文献
178.
DAI Jian S 《中国科学E辑(英文版)》2009,52(4):975-985
This paper presents a classification on the workspaces of planar serial three-link manipulators, that is, position workspace
and orientation angle workspace. Position workspace indicates the region reached by the reference point on the end-effector.
Orientation angle workspace indicates a set of angle ranges by which the end-effector can reach with certain orientation for
every point in the reachable position workspace. By introducing a virtual equivalent mechanism, reachable position workspace
can be divided into several Grashof intervals and non-Grashof intervals. The calculation equations of orientation angle workspace
are deduced in three situations according to the relationships among four link lengths in the virtual four-bar chain. Three
examples are given for three kinds of relationship of link lengths. The orientation angle workspace of extended groups, that
is, two of the three link lengths equal, and the orientation angle workspace when the reference point on the end-effector
moves along a non-radial direction are also discussed. A program is developed to calculate orientation angle workspaces and
output variation curves of orientation angle workspace and key data within the position workspace. The approach and program
in this paper can be used for fast calculation and identification of the variation rule of the orientation angle workspace
of any given planar serial three-link manipulator on the basis of its link parameters, and for the design of a highly dexterous
serial manipulator with proposed link relations.
Supported by the Natural Science Foundation of Shanxi Province (Grant No. 20041070) 相似文献
179.
DongJie Guo HaiTao Ding Haiju Wei Qingsong He Min Yu ZhenDong Dai 《中国科学E辑(英文版)》2009,52(10):3061-3070
This paper reports a new technique to fabricate an ion-exchange polymer-metal composite (IPMC) actuator. This technique is based on a hybrid organic-inorganic composite membrane. In the fabrication course, silica oxide particles, prepared from hydrolysis of tetraethyl orthosilicate in situ with sol-gel reaction, co-crystallize with perfluorosulfonate acid (PFSA) ionomer. Attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) analyses demonstrate that a highly water-saving hybrid mem... 相似文献
180.
In order to restrain the mid-spatial frequency error in magnetorheological finishing (MRF) process, a novel part-random path is designed based on the theory of maximum entropy method (MEM). Using KDMRF-1000F polishing machine, one flat work piece (98 mm in diameter) is polished. The mid-spatial frequency error in the region using part-random path is much lower than that by using common raster path. After one MRF iteration (7.46 min), peak-to-valley (PV) is 0.062 wave (1 wave =632.8 nm), root-mean-square (RM... 相似文献