Wire electrical discharge machining of ASP30 tool steel

Wire electrical discharge machining is a non-traditional cutting process for machining of hard and high strength materials. This study analyzed the effects of the main input parameters of wire electrical discharge machining of ASP30 steel (high alloyed Powder metallurgical [PM] high speed steel) as the workpiece on the material removal rate and surface roughness. The input parameters included spraying pressure and electric conductivity coefficient of the dielectric fluid, linear velocity of the wire and wire tension. The machined surface quality was evaluated using SEM pictures. Results indicated that increasing the spraying pressure of dielectric fluid leads to a higher material removal rate and surface roughness and that increasing the wire tension, linear velocity of wire, and electric conductivity of the dielectric fluid decreases the material removal rate and surface roughness.

     

数值模拟铸件充型过程中的液/固两相流动

铸造过程中熔融金属内的固体渣粒的运动轨迹是非常重要的。文中给出了粒子传输轨迹的数学模型,该数学模型采用显示法来确定粒子的位置。模拟研究结果与用其它数学模型的模拟结果比较,吻合良好。该模型可用于固体粒子位置的确定,并应用到SUTCAST软件中。     

Two meta-heuristics for three-stage assembly flowshop scheduling with sequence-dependent setup times

In this paper, we consider a three-stage assembly flowshop scheduling problem with bi-objectives, namely the mean flow time and maximum tardiness. This problem can be considered as a production system model consisting of three stages: (1) different production operations are done in parallel, concurrently and independently, (2) the manufactured parts are collected and transferred to the next stage, and (3) these parts are assembled into final products. In this paper, sequence-dependent setup times and transfer times are also considered as two important presumptions in order to make the problem more realistic. We present a novel mathematical model for a production system with a new lower bound for the given problem. Obtaining an optimal solution for this type of complex, large-sized problem in reasonable computational time by using traditional approaches and optimization tools is extremely difficult. Thus, we propose two meta-heuristics, namely simulated annealing and tabu search, to solve a number of test problems generated at random. Finally, the computational results are illustrated and compared in order to show the efficiency of the foregoing meta-heuristics.     

Performance evaluation of modified rotating-jet electrospinning method by investigating the effect of collector size on the nanofibers alignment

Modified rotating-jet electrospinning method (MRJM) is a new electrospinning technique with a novel setup including two metallic concentric hollow cylinders for generating highly aligned fibers. In this report, an experimental study was carried out to evaluate the effectiveness of MRJM for generating highly aligned nanofibers. For this purpose, the effect of voltage in the range of 10–22 kV, inner collector diameter in the range of 20–50 cm, and outer collector diameter in the range of 30–60 cm, on alignment degrees of electrospun fibers were explored and the results for each set of parameters were compared with those obtained for rotating-jet electrospinning method (RJM). The obtained results indicated that the alignment degrees of electrospun fibers in MRJM were significantly higher than those of RJM. The maximum achievable alignment degree in MRJM was around 82 % that was higher than the corresponding maximum value (40 %) of RJM. Although the effect of applied voltage on the degree of alignment in MRJM was observed to be negligible, it was experimentally proved that by manipulating the outer cylinder diameter, the degree of alignment can be increased up to 20 %. To achieve a conceptual understanding of the reason for significant influence of the outer cylinder on the elecrospinning performance, a formula was derived according to the Gauss’s law in the last part of this paper that relates the electric field strength inside the region between the inner cylinder and the spinneret to the radii of inner and outer cylinders.     

组合剪力墙的滞回性能评价

组合型钢剪力墙刚度大、延性好,在土木工程中应用广泛。组合型钢剪力墙一般通过铺设与钢板连接的混凝土层或纤维增强复合板形成。本试验和数值研究主要分析剪力钉间距、中梁刚度、梁柱连接方法对组合型钢剪力墙性能的影响。结果表明:增大剪力钉间距可减小荷载-位移曲线的斜率,并提高结构韧性。中梁刚度和梁柱连接对组合型钢剪力墙性能的影响是非常微小的,可以忽略。     

Self-healing ability and adhesion strength of capsule embedded coatings—Micro and nano sized capsules containing linseed oil

Urea–formaldehyde (UF) capsules were synthesized in micro and nano sizes, containing linseed oil (LO). The micro- and nanocapsules were incorporated through epoxy coatings and the coatings were applied on C-steel panels. Then the self-healing performance of the coatings was investigated. The corrosion resistance, adhesion strength and its retaining after immersion of nanocapsule incorporated coatings were compared with the optimum microcapsule incorporated ones.     

Static Response of Reinforced Soil Retaining Walls with Nonuniform Reinforcement

The structural response of reinforced‐soil wall systems with more than one reinforcement type (nonuniform reinforcement) is investigated using a numerical approach. The selected reinforcement types and mechanical properties represent actual polyester geogrid and woven wire mesh products. The model walls are mainly of wrapped‐face type and have different reinforcement lengths, arrangements, and stiffness values. Additional wall models with tiered and vertical gabion facings are included for comparison purposes. The numerical simulation of wall models has been carried out using a finite difference‐based program and includes sequential construction of the wall and placement of reinforcement at uniform vertical spacing followed by a sloped surcharge. The wall lateral displacements and backcalculated lateral earth pressure coefficient behind the facing in all nonuniform reinforcement wall models show a clear dependence on relative stiffness values of reinforcement layers at different elevations. An equation is proposed that can be used to predict the maximum reinforcement load in nonuniform reinforced wrapped‐face walls of given backfill types and reinforcement configurations similar to those investigated in this study.     

硫化铅纳米粒子的三阶非线性光学特性研究

针对硫化铅(PbS)特殊的三阶非线性光学特性,本文在水溶液里合成了PbS纳米粒子.紫外-可见光谱显示,由于使用了封端剂,合成的样品更加稳定.用紫外-可见吸收光谱和X射线衍射斑研究了PbS纳米粒子的特性,结果表明,由于纳米粒子尺寸减小,其吸收光谱显示极大的蓝移.利用Seherre方程估计PbS粒子的平均粒径约为8.2 n...     

Numerical study of blowing and suction slot geometry optimization on NACA 0012 airfoil

The effects of jet width on blowing and suction flow control were evaluated for a NACA 0012 airfoil. RANS equations were employed in conjunction with a Menter’s shear stress turbulent model. Tangential and perpendicular blowing at the trailing edge and perpendicular suction at the leading edge were applied on the airfoil upper surface. The jet widths were varied from 1.5% to 4% of the chord length, and the jet velocity was 0.3 and 0.5 of the free-stream velocity. Results of this study demonstrated that when the blowing jet width increases, the lift-to-drag ratio rises continuously in tangential blowing and decreases quasi-linearly in perpendicular blowing. The jet widths of 3.5% and 4% of the chord length are the most effective amounts for tangential blowing, and smaller jet widths are more effective for perpendicular blowing. The lift-to-drag ratio improves when the suction jet width increases and reaches its maximum value at 2.5% of the chord length.     

Indoor geolocation in the absence of direct path

Severe multipath in indoor areas causes undetected direct path (UDP) conditions, which pose a serious challenge to the design of robust precision indoor geolocation systems. Based on a scenario on the third floor of the Atwater Kent Laboratory at the Worcester Polytechnic Institute, we explain the reason for frequent absence of direct path, and introduce and analyze the effectiveness of two novel approaches to mitigating the large ranging errors caused by UDP conditions. The first technique exploits nondirect paths for ranging, while the second approach relies on cooperative localization for wireless sensor and ad hoc networks