An investigation on the soldering of Al 3003/Zn sheets

In this research, Al 3003/Zn sheets with different Zn layer thicknesses (as filler layer) have been soldered to the monolithic Al 3003 sheets. The effects of Zn layer thickness and soldering time at the peak temperature on the joint strength of soldered Al 3003 alloy by pure Zn filler (as the soldering sheets) have been evaluated. Furthermore, microstructure and fracture mechanism of Al 3003/Zn/Al 3003 soldered joints have been studied. The results indicate that by decreasing the Zn layer thickness and increasing the holding time at the peak temperature of soldering, the joint strength improves. Additionally, microscope examinations show that the fracture type of the Al 3003/Zn/Al 3003 soldered joint is predominantly brittle.     

Realization of a bragg reflection filter wavemeter

We present the preliminary results of a metrological standard for fiber Bragg gratings. This device is based on well-established wavemeter concepts and allows for the a priori determination of Bragg resonances that are verifiable and accurate. Although the concept is demonstrated here with small-fringe-number samplings, the production and detection of images of 50,000 metering fringes was easily accomplished with a nonidealized imaging system. Thus, since the system is characteristically similar to a standard wavemeter, increased fringe counts produce accurate frequency counter ratios for the determination of Bragg resonances, allowing for its application as a universal metering tool for many holographic systems.     

Calibration of a computer-controlled precision wavemeter for use with pulsed lasers

The design of a pulsed wavemeter to monitor the high-precision tuning of pulsed (as well as cw) laser sources is presented. This device is developed from a combination of silver-coated Fabry-Perot etalons with various plate spacings. These etalons provide stepwise refinement of the wavelength to be measured. The wavemeter is controlled by a computer through a CAMAC interface, which measures the absolute wavelength in the visible with an accuracy of 2 parts in 10(8). The time required for data acquisition and computation to measure the refined wavelength with a single 2-MHz CPU is less than 100 ms. We describe the calibration of the instrument over the wavelength range 400-850 nm. We obtain the required calibration lines by locking lasers on hyperfine transitions of iodine, uranium, rubidium, and cesium. Methods to reduce the number of calibration lines required for calibration of the system are described. The expected wavelength-dependent phase shift of the silver coatings is compared with that measured for the etalon following calibration. The differences are larger than expected because of either optical aberations or the use of centroids to measure the fringe position.     

Experimental investigation and finite element modeling on profile forming of conical component using Al 3003(O) alloy

Profile forming of sheet metal is a special technique that offers flexibility and cost-effectiveness in the metal forming process, requiring no high capacity presses or set of dies, thus meeting the ever increasing demand for small batch production and rapid prototyping. This paper demonstrates the formation of sheet metal part using the CNC controlled hemispherical tool and analyses the various parameters underlying this mechanism – like maximum wall angle, surface roughness (Ra) and thinning of sheet. Analysis of the microstructure is carried out using Scanning electron microscopy and Energy-dispersive X-ray spectroscopy microanalysis test. In this study, Aluminum sheet of grade Al 3003(O) with 1 mm and 1.25 mm thickness is used as a work piece. The paper also presents an explicit numerical simulation using the standard finite element code ABAQUS and the experimental and numerical results are validated.     

Driver behavior in car-to-pedestrian incidents: An application of the Driving Reliability and Error Analysis Method (DREAM)

To develop relevant road safety countermeasures, it is necessary to first obtain an in-depth understanding of how and why safety-critical situations such as incidents, near-crashes, and crashes occur. Video-recordings from naturalistic driving studies provide detailed information on events and circumstances prior to such situations that is difficult to obtain from traditional crash investigations, at least when it comes to the observable driver behavior. This study analyzed causation in 90 video-recordings of car-to-pedestrian incidents captured by onboard cameras in a naturalistic driving study in Japan. The Driving Reliability and Error Analysis Method (DREAM) was modified and used to identify contributing factors and causation patterns in these incidents. Two main causation patterns were found. In intersections, drivers failed to recognize the presence of the conflict pedestrian due to visual obstructions and/or because their attention was allocated towards something other than the conflict pedestrian. In incidents away from intersections, this pattern reoccurred along with another pattern showing that pedestrians often behaved in unexpected ways. These patterns indicate that an interactive advanced driver assistance system (ADAS) able to redirect the driver's attention could have averted many of the intersection incidents, while autonomous systems may be needed away from intersections. Cooperative ADAS may be needed to address issues raised by visual obstructions.     

3003铝合金动态再结晶实验研究

采用Gleeble-1500热模拟试验机对3003铝合金进行变形温度为300～500℃、应变速率为0.01～10.0s-1的高温等温压缩实验,由真应力-真应变曲线计算应变硬化速率,并采用截线法测量热压缩后平均晶粒尺寸,结果表明:3003铝合金动态再结晶临界应变εc随着Z参数的增大而提高,合金发生动态再结晶的临界条件为:...     

3003铝合金蠕变行为与本构方程

研究了3003铝合金冷轧变形后再结晶组织控制和175~250℃、外加应力25~50 MPa条件下3003铝合金的蠕变行为。采用弹性模量归一化应力幂律蠕变本构方程,对实验数据进行线性拟合,建立了能够较好描述稳态蠕变速率与应力、温度三者之间关系的本构方程。结果表明:采用350℃和600℃的两步再结晶退火,可获得有利于提高合金蠕变性能的长条状再结晶组织;温度越高,应力增加对稳态蠕变速率增加的贡献越大;不同温度下3003铝合金的蠕变机制不同,175℃时,应力指数n=3.5,蠕变主要由位错滑移控制;在200~250℃范围内,n处于5.1~8.6之间,蠕变主要由位错攀移控制。     

An extension of the application of transmission line modelling (TLM) to thermal diffusion to include non-infinite heat sources

The modelling of heat transfer from a moving gaseous atmosphere by the TLM technique is described. For the case of very rapidly moving gas, results are compared with those derived from finite element analysis.     

Natural and man-made cellulose fibre-reinforced poly(lactic acid) (PLA) composites: An overview about mechanical characteristics and application areas

The paper describes the production and the mechanical characteristics of composites made completely of renewable raw materials. Composites of different kinds of natural fibres like cotton, hemp, kenaf and man-made cellulose fibres (Lyocell) with various characteristics were processed with a fibre mass proportion of 40% and poly(lactic acid) (PLA) by compression moulding. Additionally, composites were made of fibre mixtures (hemp/kenaf, hemp/Lyocell). The composites were tested for tensile strength, elongation at break, Young’s modulus and Charpy impact strength. Their characteristics varied markedly depending on the characteristics of the raw fibres and fibre bundles and fibre mixtures used. While kenaf and hemp/PLA composites showed very high tensile strength and Young’s modulus values, cotton/PLA showed good impact characteristics. Lyocell/PLA composites combined both, high tensile strength and Young’s modulus with high impact strength. Thus, the composites could be applied in various fields, each meeting different requirements.     

Structure stability of AA3003 alloy with ultra-fine grain size

The study on the structure stability of AA3003 alloy produced by an intense plastic straining process named accumulative roll bonding (ARB) has been conducted. The results show that continuous recrystallization took place in the ARBed 3003 alloy with increasing the annealing time at 250°C and increasing the annealing temperature to 275°C. While, discontinuous recrystallization began in some regions after 300°C annealing, and nearly finished after 400°C annealing. Furthermore, an unusual tensile behavior was observed in this alloy after annealing at 250–275°C. The Hall-Petch dependence was observed in the plot of microhardness versus d ^–1/2 of the ARBed 3003 alloy, but its dependence slope was changed. The ultra-fine grains (<1 m) formed in the ARBed 3003 alloy can be stable until annealing at 250°C for 1 h, and the fine grains (<2 m) can be stable until annealing at 275°C for 1 h. Therefore, grain structure formed in the ARBed 3003 alloys after intense plastic strain is reasonably stable. In addition, the mechanism of structure stability and mechanical behavior were also discussed.     

Mn、Fe含量对3003铝合金铸锭均匀化行为的影响

通过电导率测试、扫描电子显微镜等观察分析,研究了不同Mn、Fe含量对3003合金铸锭和均匀化组织的影响。3003合金铸锭中有明显的波纹状Mn偏析,晶界处有粗大的α-Al(Fe,Mn)Si或Al₆(Fe,Mn)初生相。Fe含量由0.12%(质量分数)升高至0.30%,铸锭平均晶粒尺寸由257 μm减小为108 μm,初生相面积分数由1.28%升高至3.75%;Mn含量越高,合金电导率值越低。均匀化升温阶段,析出相主要受形核和长大过程控制,并伴随较高温度下析出相的部分回溶;600 ℃保温阶段,析出相以Ostwald熟化和原子长程扩散两种机制发生粗化,尺寸不断增大,数量减少;合金均匀化晶界附近有无析出带形成。合金Mn含量由1.15%升高至1.60%,析出相回溶温度由500 ℃升高至550 ℃,600 ℃保温12 h完成后,析出相尺寸也由149.0 nm升高至342.5 nm;高Fe低Mn(0.30%Fe,1.15%Mn)合金晶内析出相分布均匀,而低Fe高Mn(0.12%Fe,1.60%Mn)合金晶内析出相呈不均匀分布,晶粒心部及枝晶干处贫Mn区析出相数量较少。     

An electron-microscopic study of precipitation (exsolution) in an amphibole (the hornblende-grunerite system)

Transmission, analytical and high-voltage electron microscopy have been used to study the distribution of phases in the naturally occurring silicate minerals hornblende and grunerite. These two minerals belong to the amphibole group and previous analytical work has suggested the existence of a miscibility gap between them involving the segregation of calcium. The minerals in the specimens studied are coarse-grained, having crystallized slowly during metamorphism.Large lamellar precipitates are present in both phases. These precipitates form on (100) and (¯101) planes of the matrix and have remained coherent. Steps are present on the broad faces of these lamellae, suggesting that they have thickened by the propagation of ledges as observed in metal alloy systems. These features are common to both phases, but the grunerite matrix contains an additional set of fine, coherent precipitates which have formed at a later stage and show distinct precipitate-free zones around the earlier precipitates. Analytical microscopy has been used to confirm qualitatively that the precipitation involves segregation of calcium.     

Optimization of GTAW Al 3003 weld using fabricated nanocomposite filler metal

Novel Al–3 wt.% TiO₂ (fillers) nanocomposite has been successfully fabricated by accumulative roll bonding method to join Al 3003 alloy with the parameters of gas tungsten arc welding process such as the shielding gas flow rate (G), the welding speed (S), and the current (I) identified by response surface methodology. After preparation of weldment, studies involving X-ray diffraction and advanced electron microscopy techniques (scanning electron microscope and transmission electron microscope) have been carried out. FESEM has revealed the presence of second-phase hard ceramic particles which are embedded homogeneously in the matrix material. Energy dispersive spectroscopy analysis indicates the absence of foreign particles other than Al, Ti, and oxides. Further, the results show that the increase in mechanical properties (hardness and ultimate tensile strength) of the weldment is due to grain refinement and uniform distribution of TiO₂ nanoparticles. The analysis of variance test identified the welding speed as a significant parameter on the homogeneous distribution of TiO₂ particles followed by current and gas flow rate in sequential order.     

聚二甲基硅氧烷的应用研究进展

概述了聚二甲基硅氧烷在杂化材料、阻燃材料、渗透膜、乳液、气相色谱中的固定相、改性其它聚合物、微流控芯片及稀土高分子材料中的研究和应用进展,并指出其今后研究开发的重点.     

聚四氟乙烯的改性及应用

本文从聚四氟乙烯的组成、结构及物理化学特性、成型加工技术等方面说明了聚四氟乙烯改性的必要性 ,并对其表面改性、填充改性及共混改性作了较详细的介绍。认为聚四氟乙烯薄膜复合技术及改性技术将是未来聚四氟乙烯的主要发展方向 ,最后对聚四氟乙烯及其改性制品的应用作了介绍。     

Solidification Studies of 3003 Aluminium Alloys with Cu and Zr Additions

The effects of Cu and Zr additions, on the microstructure formation, precipitation and ingot cracking, in commercial 3003 Al alloys have been studied. The investigation was carried out by characterizing the grain structure in DC-cast rolling ingots, and studying the solidification microstructure of Bridgman directionally solidified samples. To better understand the influence of the different Cu and Zr contents on the phase precipitations, differential thermal analysis (DTA) experiments were performed. Results from the ingot microstructure analysis show that in commercial alloys with relatively high contents of Cu and Zr, no significant differences in measured grain sizes compared to conventional 3003 Al alloys could be found. However, only Zr containing alloys exhibited significantly larger grain sizes. Increased grain refiner and/or titanium additions could compensate for the negative effects on nucleation normally following Zr alloying. Different types of precipitates were observed. Based on DTA experiments, increased Cu and Zr contents resulted in the formation of Al2Cu phase, and increased solidification range. It was also found that increased Mn content favors an early precipitation of Al6(Mn,Fe) giving relatively coarse precipitates. It was concluded that the Cu alloying has a detrimental effect on hot tearing.     

Tribological application of molecular deposition (MD) films

In this paper, the nanofriction and nanolubrication behaviors of different MD films on the Au substrate were systematically studied. The experimental results indicated that the MD films presented similar nanofriction properties when they had a same terminal. It was also found that the process of the anionning and the depositing of a monolayer MD film on a Au substrate and the process of decorating an alkyl-terminal to MD film surfaces were all capable of lowering the frictional force and improving the nanolubrication property. Moreover, the MD film decorated with alkyl chains had lower frictional forces than the undecorated MD films. Accordingly, it provided us a significant thought to seek for a new nanolubrication film.