高速GMAW驼峰焊道形成过程熔池图像识别

针对高速驼峰焊道形成过程中熔池的变化规律,采用CCD视觉传感系统跟踪采集. 提出了一种基于模糊C-均值聚类(fuzzy C-means,FCM)协作主动轮廓(chan-vese,CV)模型的熔池图像分割方法,对高速焊接过程中的熔池图像进行图像分割. 结果表明,驼峰的形成过程中,熔池长度的阶跃变化是反映驼峰形成的主要图像特征. 将熔池长度序列拟合成波形,采用Symlets2号小波进行分解,发现d₂级小波分解能更好地识别熔池长度的阶跃变化. 对d₂级小波细节能量设定阈值,获取反映熔池长度阶跃变化的尖峰突起特征信号,能很好地识别驼峰缺陷的形成,初步实现了驼峰焊道的监测控制.     

Effects of nitrogen implantation on low cycle fatigue behavior of ferritic Fe-24Cr-4Al stainless alloy

The effects of nitrogen implantation on cyclic deformation response, near-surface dislocation sub-structure, surface slip band formation, crack initiation, and fatigue life under low cycle fatigue of the ferritic Fe-24Cr-4Al stainless alloy were investigated. Implantation was carried out at an energy of 65 keV and at a fluence of 2 × 10¹⁷ ions/cm². Nitrogen implantation resulted in a substantial cyclic hardening in the alloy. Homogeneous planar dislocation arrangements were formed in the near-surface region of implanted specimens after fatigue, while dislocation loop debris and patches were developed in the un-implanted specimens. Moreover, formation of persistent slip bands (PSBs) was greatly suppressed in the surface of the implanted specimens. Nitrogen implantation also resulted in an alteration of the crack initiation mode from the grain boundary to the surface penetration of the PSBs nucleated below the surface layer. Fatigue life improvements after nitrogen implantation could only be obtained when the PSBs were not only suppressed but also homogenized in the implanted surface layer.     

Short-term effects of a high-sucrose diet on plasma lipid, lipoprotein cholesterol, tissue lipoprotein lipase and hepatic triglyceride lipase in rats

Short-term (2 weeks) effects of a high-sucrose diet on plasma lipids, lipoproteins, tissue lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) activities were investigated in rats. Three days of sucrose feeding significantly increased plasma TG (42 +/- 3 mg/dl vs. 56 +/- 2 mg/dl, p = 0.032), while TC increased significantly after 10 days of the diet (50 +/- 2 mg/dl vs. 62 +/- 2 mg/dl, p = 0.0001). HDL-C increased significantly after 3 days of sucrose feeding (36.2 +/- 0.9 mg/dl vs. 42.4 +/- 2.7 mg/dl, p = 0.011). Although LDL-C tended to decrease on days 3, 7 and 10, these changes were not significant. The plasma glucose level did not change during the study. Increased LPL activity in adipose tissue and decreased enzyme activities in skeletal and heart muscles were observed. Adipose tissue LPL returned to the baseline value after 14 days of the diet treatment, while LPL in skeletal and heart muscles remained at the decreased level. HTGL and HTGL/total liver lipase activities were significantly increased after 14 days of the diet. The different responses of lipase activities in various tissues may help to regulate serum lipid and lipoprotein levels in sucrose-fed rats.     

Creep and low-cycle fatigue behavior of ferritic Fe-24Cr-4Al alloy in the dynamic strain aging regime: Effect of aluminum addition

Creep and low-cycle fatigue behavior of ferritic Fe-24Cr-4Al alloy was studied in the temperature range of 673 to 873 K, where dynamic strain aging (DSA) occurrence was found. The DSA of the alloy manifested in the form of serrated flow, negative strain rate sensitivity, and the peak or plateau in the variations of yield strength (YS) and ultimate tensile strength (UTS) with temperature. The characteristic creep behavior of the alloy was experimentally verified as that for a class I solid solution. However, this ferritic alloy showed an anomalous high stress exponent (n=5.7) and high activation energy (Q _c =285 kJ/mol) of the secondary creep, which were commonly exhibited by class II solid solutions. During cyclic deformation, the alloy displayed serration in the stress-strain hysteresis loops, increased cyclic hardening, and enhanced planarity of dislocations. On the basis of the observed experimental results and proper analysis, it was proposed that there was strong elastic interaction between solute aluminum atoms and dislocations in the DSA temperature domain. The anomalous creep and fatigue features were interpreted in terms of the interaction of aluminum with the dislocations.     

A Behavior-Learned Cross-Reactive Sensor Matrix for Intelligent Skin Perception

Mimicking human skin sensation such as spontaneous multimodal perception and identification/discrimination of intermixed stimuli is severely hindered by the difficulty of efficient integration of complex cutaneous receptor-emulating circuitry and the lack of an appropriate protocol to discern the intermixed signals. Here, a highly stretchable cross-reactive sensor matrix is demonstrated, which can detect, classify, and discriminate various intermixed tactile and thermal stimuli using a machine-learning approach. Particularly, the multimodal perception ability is achieved by utilizing a learning algorithm based on the bag-of-words (BoW) model, where, by learning and recognizing the stimulus-dependent 2D output image patterns, the discrimination of each stimulus in various multimodal stimuli environments is possible. In addition, the single sensor device integrated in the cross-reactive sensor matrix exhibits multimodal detection of strain, flexion, pressure, and temperature. It is hoped that his proof-of-concept device with machine-learning-based approach will provide a versatile route to simplify the electronic skin systems with reduced architecture complexity and adaptability to various environments beyond the limitation of conventional “lock and key” approaches.     

Some aspects of the Aluminide coating on Fe-18Cr alloy

Diffusion aluminide coating was formed on Fe-18Cr alloy by the pack cementation method. Electron and X-ray diffraction techniques were used to identify the phases formed on the aluminide coating layer. This coating layer was found to consist of the FeAl and Fe₃Al phases. Furthermore, coated specimens were exposed to air at 1200°C for 60 hours, and the oxide scales formed on the coating layer consist of randomly oriented spinel Fe(AlCr)₂O₄ and α-Al₂O₃.     

Electrical properties of low density polyethylene/ZnO nanocomposites: The effect of thermal treatments

Low density polyethylene (LDPE)/ZnO nanocomposites were prepared by melt compounding followed by annealing or quenching treatment. Electrical properties of the thermally treated nanocomposites were investigated. The results showed that thermal treatments exerted a pronounced effect on the electrical properties of LDPE/ZnO nanocomposites. The dielectric constant of annealed LDPE/ZnO nanocomposites at various ZnO contents was higher than that of quenched nanocomposites. In sharp contrast, the resistivity of annealed LDPE/ZnO nanocomposites was considerably lower than that of quenched samples. The frequency dependence of dielectric constant was much pronounced for both the annealed and quenched LDPE/ZnO nanocomposites associated with the formation of ZnO network as the ZnO volume content reached 52 vol %. The structure–property relationship of the nanocomposites is discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1436–1444, 2006