Weld temperature effects during friction stir welding of dissimilar aluminum alloys 6061-t6 and 7075-t6

The objective of this work is to establish nominal friction stir [butt] welding process parameters for joining 4.76-mm-thick aluminum alloys 6061-T6 and 7075-T6 and to improve the joint quality via programmed tool offsets. In addition, dynamic tool–workpiece interface temperatures are measured during welding and used to explain the effects of alloy placement and weld tool offset from the joint. Weld tool offsets into the retreating side AA7075 increase the measured tensile strength of the dissimilar joint. The increased joint strength is facilitated by lower average weld temperatures with increasing amount of AA7075 stirred into the nugget.     

伊维菌素在电喷雾质谱中的行为及其机理的研究

用电喷雾飞行时间质谱 (ESI TOF MS)研究了伊维菌素在ESI正、负离子检测方式下的加合和碎裂行为。正离子检测方式下的最佳有机溶剂浓度为5 0 %甲醇。在nozzle电压为 12 0V时 ,[M +NH4]+ 响应最强 ,而 [M +Na]+ 和 [M +K]+ 响应在 30 0V达最大值。伊维菌素在ESI MS中 ,得不到 [M +H]+ 峰。负离子的最佳有机溶剂浓度为 90 %甲醇 ,低nozzle电压时加合离子的强度很高 ,主要形成 [M +Cl]- 、[M +HCOO]- 、[M +CH3COO]- 和 [M +C3H5 O3]- ,加大nozzle电压 ,碎裂峰强度增加 ,主要是失掉一个氢 ,以及在此基础上再失掉一个或两个水分子、糖基 ,及反Diels Alder碎片的峰。当nozzle电压为 2 0 0V时 ,[M -H]- 峰达最大值。     

Parametric study of the dry sliding wear behaviour of AA6082-T6/SiC and AA6082-T6/B<Subscript>4</Subscript>C composites using RSM

In this paper a parametric study of the wear behaviour of Aluminum matrix composites has been carried out. AA6082-T6/SiC and AA6082-T6/B₄C composites were fabricated using stir casting technique. The percentage of reinforcement was taken as 5, 10, 15 and 20 wt.% for both SiC and B₄C particulates. Dry sliding wear tests were conducted using pin-on-disc apparatus at room temperature and process optimization was done using Response surface methodology (RSM). Weight percentage (wt.%) of reinforcement, sliding speed, load and sliding distance were the four process parameters considered to analyse these composites wear behaviour. Analysis of variance (ANOVA) showed that sliding distance exerted the highest contribution (60.24 %) to AA6082-T6/SiC wear, followed by sliding speed (14.28 %), load (11.88 %) and reinforcement content (4.31 %). The same trend was found in AA6082-T6/B₄C composites with slightly different contribution values, namely sliding distance (63.28 %), sliding speed (14.02 %), load (10.10 %) and reinforcement content (4.05 %). RSM analysis revealed that increases in the reinforcement content and sliding speed reduce the wear rate in both composites. On the other hand, increases in load and sliding distance led to higher AA6082-T6/SiC and AA6082-T6/B₄C composites wear. The two predictive models were validated by conducting confirmation tests and certified that the developed wear predictive models are accurate and can be used as predictive tools for wear apllications.     

基于自导向副弹塑性变形的深孔轴线偏斜研究

基于自导向机理,分析了导向副的载荷以及接触状态,借助Hertz接触理论、弹塑性变形理论,建立了自导向副的变形模型以及深孔轴线偏斜的数学预测模型。结合理论模型和钻削实验确定了钻削过程中导向副的实际接触状态,并研究了导向条滞后量和工件材料对轴线偏斜的影响。研究表明：滞后量越大,轴线偏斜越大;材料刚度越小,轴线偏斜越大。     

6061/A356异种铝合金脉冲MIG搭接焊*

利用直流脉冲MIG焊接技术,进行6061变形铝合金与A356铸造铝合金板材的搭接焊接,并分析接头的力学性能、微观组织及元素分布。拉伸试验结果表明,当A356铸造铝合金板在上,6061变形铝合金板在下,焊枪行走速度为10 mm/s时,搭接接头抗拉强度最高,为95 MPa。接头拉伸试样的断裂位置都位于焊缝区,断裂形式主要为混合型断裂。微观组织及元素分析结果表明,在A356铝合金一侧的部分熔融区内发生Fe和Mg元素偏聚,形成了片状Al-Fe-Si相和颗粒状Al-Fe-Mg-Si相,这两种富Fe相会削弱接头性能。在6061铝合金一侧的部分熔融区内产生了晶界液化,形成了Al-Mg-Si-Cu相+Al固溶体贫化区的液化组织,且该相周围有Fe元素偏聚。三角区是接头中最薄弱的位置,接头拉伸试样均起裂于此并最终断裂于焊缝。     

Ferrule-top atomic force microscope

Ferrule-top cantilevers are a new generation of all-optical miniaturized devices for utilization in liquids, harsh environments, and small volumes [G. Gruca et al., Meas. Sci. Technol. 21, 094033 (2010)]. They are obtained by carving the end of a ferruled fiber in the form of a mechanical beam. Light coupled from the opposite side of the fiber allows detection of cantilever deflections. In this paper, we demonstrate that ferrule-top cantilevers can be used to develop ultra compact AFMs for contact mode imaging in air and in liquids with sensitivity comparable to that of commercial AFMs. The probes do not require any alignment procedure and are easy to handle, favoring applications also outside research laboratories.     

Dynamic deformation behavior of aluminum alloys under high strain rate compressive/tensile loading

Mechanical properties of the materials used for transportations and industrial machinery under high strain rate loading conditions such as seismic loading are required to provide appropriate safety assessment to these mechanical structures. The Split Hopkinson Pressure Bar (SHPB) technique with a special experimental apparatus can be used to obtain the material behavior under high strain rate loading conditions. In this paper, dynamic deformation behaviors of the aluminum alloys such as A12024-T4, A16061T-6 and A17075-T6 under both high strain rate compressive and tensile loading conditions are determined using the SHPB technique.     

The Pressure–Viscosity Coefficient of Several Ionic Liquids

The choice of cation and anion in an ionic liquid (IL) as well as the design of ion side chains determine the fundamental properties of ILs, which permits creating tailor-made lubricants and lubricant additives. So, the study of the influence of molecular structure on thermophysical properties of ionic liquids is essential for their use in lubrication. Recent results from the literature, essentially based on ammonium, phosphonium, or imidazolium cations, are promising from the tribological point of view, but still new investigations should be performed, for example, in elastohydrodynamic lubrication (EHL), for which calculations of the universal pressure–viscosity coefficient, α _film , and central thickness are needed. In this work viscosity and density data from the literature on broad pressure and temperature ranges for the ILs [C₄C₁im]PF₆, [C₄C₁im]Tf₂ N, [C₄C₁im]BF₄, [C₈C₁im]PF₆, [C₈C₁im]BF₄, [C₆C₁im]PF₆, and [C₆C₁im]Tf₂ N are used to determine their α _film values over a wide temperature range. The American Gear Manufacturers Association relation of the central thickness with the pressure viscosity coefficient is used to estimate the film-generating capability of these lubricants. Furthermore, an overview of the literature data on tribological and physical properties of the ionic liquids is presented. Presented partially at the LUBMAT 08 Conference, San Sebastian, Spain, June 2–4, 2008.     

Design and experimental study of an end effector for robotic drilling

This paper presents the development of a drill end effector for use on industrial robots. The end effector has low weight and high rigidity. The drill end effector is fully programmable and will realize different drilling mode. The real-time force feedback can detect dull or broken bits, drill to breakthrough, and plot thrust force while drilling. Additionally, the end effector can also be equipped with a coolant/lubricant device. Based on the drill end effector, an experimental study on dry drilling of Ti-6Al-4V alloy and 7075-T6 alloy bimetal stacks was performed by using an uncoated cemented carbide drill. The hole quality (hole size, surface roughness) and thrust force were evaluated at various spindle speeds, feed rates, stacking sequence, and clamp force. This study indicates that the spindle speed and feed rate have an effect on the hole quality and thrust force by means of changing the temperature and plastic deformation of cutting zone. The results show that drilling 7075-T6 alloy firstly would be most efficient because of the high hole quality and the low thrust force. It was also found that high clamp force is helpful to improve the hole quality.     

Friction stir butt welding thin aluminum alloy sheets

0.8-mm-thick alclad 2024-T4 aluminum alloy sheets were friction stir butt welded. A 15-mm diameter shoulder tool was used to guarantee sufficient heat input during welding. A 0.08-mm shoulder plunge depth was adopted to reduce sheet thickness reduction. Sound joints were obtained at rotating speeds from 400 to 1000 rpm and welding speeds from 50 to 150 mm/min. A thickness reduction of 6% was achieved at 1000 rpm and 50 mm/min. Secondary phases firstly precipitated at the black lines in the stir zone (SZ). The hardness of the SZ showed a decrease about 6% compared with the base metal. A maximum tensile strength of 399.5 MPa and an elongation of 5.6% were achieved at 1000 rpm and 150 mm/min. The fracture morphologies showed typical ductile fracture mode.     

沃尼妙林在电喷雾质谱中的行为研究

采用电喷雾质谱研究沃尼妙林在正负离子模式下电离的碎裂行为。在正离子模式下进行一级质谱全扫描时,主要得到[M+H]⁺ m/z 565.7的分子离子峰,负离子模式主要得到[M-H]-m/z 563.5的分子离子峰,正离子的响应值远高于负离子。以[M+H]+为母离子进行二级质谱扫描,在适当的碰撞能下,主要得到 m/z 263.2、285.3、303.3三个碎片离子峰,其中 m/z 263.2的丰度明显高于另外2个碎片离子。并分析了沃尼妙林的碎裂机理,为进一步研究其构效关系、药物分析及残留检测等提供依据。     

Investigating the optimum molybdenum disulfide (MoS2) nanolubrication parameters in CNC milling of AL6061-T6 alloy

Aluminum 6061-T6 is an important alloy as it has dominant mechanical properties like weldability and hardness, and has the potential to be used at variable temperatures. AL6061-T6 is frequently used in the aerospace industry, as well as aircraft, automotive, and packaging food industries. Milling of Al6061-T6 is important especially to produce various product shapes for adapting to diverse applications. The aptitude of the CNC milling machine for batch production would be a noteworthy advantage. However, the demand for high quality brings attention to product quality, particularly the roughness of the machined surface because of its effect on product appearance, function, and reliability. Introducing correct lubrication to the machining zone could improve the tribological characteristics of Al6061-T6. For additional improvement, applying nanolubrication may produce superior product quality, as the rolling action of billions of nanoparticle units in the tool chip interface can significantly decrease the cutting forces. In this research work, the optimum MoS₂ nanolubrication parameters in Al6061-T6 milling to achieve the lowest cutting force, cutting temperature and surface roughness are investigated. The parameters include nanolubricant concentration, nozzle orientation and air carrier pressure. Taguchi optimization along with standard orthogonal array L₁₆(4³) are employed. Furthermore, surface roughness and cutting force are analyzed via signal-to-noise (S/N) response analysis and the analysis of variance (Pareto ANOVA) in the hopes of achieving optimum conditions and to determine which process parameters are statistically significant. Finally, optimization improvements are investigated through confirmation tests.     

液相色谱-同位素稀释质谱法准确测定人血清中葡萄糖含量

以D-[¹³C₆]葡萄糖标记物作为内标,用高效液相色谱 串联质谱法测定血清中的葡萄糖含量。向室温平衡后的血清样品中加入葡萄糖标记物,用乙醇沉淀蛋白,低温离心去除蛋白,上清液过0.22 μm有机滤膜。采用LC/MS电喷雾离子源（ESI）,正离子模式,选择离子监测模式进行检测。方法的线性相关系数R²=0.999 5,加标回收率为100.1%~102.8%,检出限为8 μg/kg,相对标准偏差0.49%。该方法的样品前处理简单,测定准确高、精密度好,可用于血清中葡萄糖含量的高准确度定值。     

An analytical approach for the prediction of forming limit curves subjected to combined strain paths

In the present work, an analytical approach for the prediction of forming limit curves is proposed to incorporate the effect of combined strain paths. The effect of combined strain paths (considering the directional dependency of pre-straining and further straining) is addressed by integrating the incremental equivalent strain expression in two stages i.e., pre-strain and subsequent loading. In each stage, the strain path is assumed to be linear and different combinations of pre-strain (uniaxial, plane-strain and equi-biaxial) are considered. Material anisotropy is taken into account in each stage. The predictions of the present model are compared with the experimental results on forming limit curves under combined strain paths for Al6111-T4 [24] and are found to be in good agreement with each other.     

A Microcalorimeter Using Semiconductors as the Sensing Elements

SUMMARY

Our previous work in biochemical calorimetry has been conducted with two modified versions [1, 2] of the Calvet microcalorimeter [3, 4]. The chief features of the modified versions are the use of electroplated thermocouples, reduction in overall size of the calorimeter and equilibration time, and mode of initiating the reaction.     

Direct calculation of modal parameters from matrix orthogonal polynomials

The object of this paper is to introduce a new technique to derive the global modal parameter (i.e. system poles) directly from estimated matrix orthogonal polynomials. This contribution generalized the results given in Rolain et al. (1994) [5] and Rolain et al. (1995) [6] for scalar orthogonal polynomials to multivariable (matrix) orthogonal polynomials for multiple input multiple output (MIMO) system.Using orthogonal polynomials improves the numerical properties of the estimation process. However, the derivation of the modal parameters from the orthogonal polynomials is in general ill-conditioned if not handled properly. The transformation of the coefficients from orthogonal polynomials basis to power polynomials basis is known to be an ill-conditioned transformation. In this paper a new approach is proposed to compute the system poles directly from the multivariable orthogonal polynomials. High order models can be used without any numerical problems.The proposed method will be compared with existing methods (Van Der Auweraer and Leuridan (1987) [4] Chen and Xu (2003) [7]). For this comparative study, simulated as well as experimental data will be used.     

电磁振动器的理论与计算

起初在我国设计电磁振动器所采用的设计理论是依据苏联学者Πотураев的结果[1],但他的结果有严重的错误及局限性,这一点已在文章[2]中指出过。本文综合作者前几篇研究报告[3][4][5][6],总结出电磁铁驱动机械电参数设计理论,给出设计公式及图表,用以纠正过去设计理论的错误,并提出电磁振动器的合理设计方法。     

Experimental studies and optimization of process parameters for burrs in dry drilling of stacked metal materials

In the drilling of stacked materials, burrs produced on both the surface layer and the interlayer have some undesirable characters with regard to assembly quality, and deburring is a time consuming and costly operation. This paper presented an experimental study on the dry drilling of Ti-6Al-4V titanium alloy and 7075-T6 aluminum alloy stacked materials, which was performed by using uncoated cemented carbide drills. The burr size was evaluated at various spindle speeds, feed rates, stacking sequences, and clamp forces. After which, the burr morphology was observed and analyzed. Finally, a new multi-objective optimization algorithm, which was derived from the game theory, was used to select optimum process parameters to minimize burr size. The best process parameters recorded in this paper were at the spindle speed of 2,000?r/min, the feed rate of 0.075?mm/r, the pressure of 0.3?MPa, and the stacking sequence of the Ti-6Al-4V titanium alloy on top of the 7075-T6 aluminum alloy.     

An investigation of optimum SiO2 nanolubrication parameters in end milling of aerospace Al6061-T6 alloy

Aluminium AL6061-T6 is a common alloy which is used for many purposes since it has the superior mechanical properties such as hardness and weldability. It is commonly used in aircraft, automotive and packaging food industries. Milling of Al6061-T6 would be a good process especially in producing varieties shape of products to adapt with different applications. The capability of the CNC milling machine to make batch production would be a noteworthy advantage. However, the demand for high quality focuses attention on product quality, especially the roughness of the machined surface, because of its effect on product appearance, function and reliability. Introducing correct lubrication in the machining zone could improve the tribological characteristic of Al6061-T6 leading to higher product quality. In this research work, the optimum SiO₂ nanolubrication parameters in milling of Al6061-T6 are investigated to achieve correct lubrication conditions for the lowest cutting force, cutting temperature and surface roughness. These parameters include nanolubricant concentration, nozzle angle and air carrier pressure. Taguchi optimization method is used with standard orthogonal array L₁₆(4)³. Furthermore, analyses on surface roughness and cutting force are conducted using signal-to-noise (S/N) response analysis and the analysis of variance (Pareto ANOVA) to determine which process parameters are statistically significant. Finally, confirmation tests were carried out to investigate the optimization improvements.     

Thermal beam of metastable krypton atoms produced by optical excitation

A room-temperature beam of krypton atoms in the metastable 5s[3/2]2 level is demonstrated via an optical excitation method. A Kr-discharge lamp is used to produce vacuum ultraviolet photons at 124 nm for the first-step excitation from the ground level 4p6 1S0 to the 5s[3/2]1 level. An 819 nm Ti:sapphire laser is used for the second-step excitation from 5s[3/2]1 to 5s[3/2]2 followed by a spontaneous decay to the 5s[3/2]2 metastable level. A metastable atomic beam with an angular flux density of 3 x 10(14) s(-1) sr(-1) is achieved at the total gas flow rate of 0.01 cm3/s at STP (or 3 x 10(17) at./s). The dependences of the flux on the gas flow rate, laser power, and lamp parameters are investigated.