Investigation of hydrodynamic deep drawing for conical�Ccylindrical cups

Forming conical parts is one of the complex and difficult fields in sheet-metal forming processes. Because of low-contact area of the sheet with punch tip in the initial stages of forming, bursting occurs on the sheet. Moreover, since most of the sheet surface in the area between the punch tip and blank holder is free, wrinkles appear on the wall of the drawing part. Thus, these parts are normally formed in industry by spinning, explosive forming, or multi-stage deep drawing processes. In this paper, forming pure copper and St14 conical?Ccylindrical cups in the hydrodynamic deep drawing process was studied using finite element (FE) simulation and experiment. The effect of pressure path on the occurrence of defects and thickness distribution and drawing ratio of the sheet was studied. It was concluded that at low pressures, bursting occurs on the contact area of sheet with punch tip. At higher pressures, the cup was formed, but the wall thickness distribution depends on the pressure path. It was also illustrated that for the pressure path with a certain maximum amount, the workpiece was formed adequately with minimum sheet thickness reduction. Internal pressures more than this maximum amounts did not affect on the thickness distribution. By applying the desired pressure path, conical?Ccylindrical cups with high deep drawing ratio were achieved.     

Production control in a failure-prone manufacturing network using discrete event simulation and automated response surface methodology

In this paper, a system consisting of a network of machines with random breakdown and repair times is considered. The machines in this system can be in one of four states: operational, in repair, starved, and blocked. Failure and repair times of the machines are exponentially distributed. Previous research on multi-machine failure-prone manufacturing systems (FPMS) has focused on systems consisting of machines in series or in parallel. This paper considers a network of machines with relationship constraints. Additionally, the system under study models work in process for multiple products, intermediate and final buffers and one type of final product. The demand rate for the final commodity is constant and unmet demand is either backlogged or lost. The objective of this control problem is to find the production rates and policies of the different machines so as to minimize the long run average inventory and backlog cost. The applied control policy is the hedging point policy that is determined by factors representing the level of buffer inventory for each machine. Obtaining analytical solutions is generally impossible for such complex systems. To simultaneously control the production rates of the machines we have therefore developed a method based on a combination of stochastic optimal control theory, discrete event simulation, experimental design and automated response surface methodology (RSM). The application of an automated RSM for Network FPMS is another contribution of this paper. The model can be extended easily to systems with age-dependent failure rates, a preventive repair maintenance policy and non-exponentially distributed up and down times.     

Seismic effects of elevating bridges with steel pedestals in the southeastern United States

Steel pedestals have been used in the southeastern parts of the United States to elevate highway bridges and decrease the likelihood of vehicle collisions with bridge decks. However, the seismic performance of bridges elevated with steel pedestals is still unknown. To investigate the effect of elevating bridges with steel pedestals, this paper uses the results of previously conducted experimental tests to model the hysteretic behavior of three types of steel pedestals in a detailed 3D finite element model of a representative bridge. One short pedestal (with a height of 500 mm) and two tall pedestals (with a height of 850 mm) are studied. The structural responses of the studied bridge with the addition of steel pedestals are compared to the structural responses of the same bridge before elevation, where elastomeric bearings support the deck. This study considers five different locations in the southeastern United States and for each of them selects 20 artificial ground motions at two hazard levels of 2% and 10% probability of exceedance in 50 years. The selected artificial ground motions are applied to the representative bridge model in four cases: one case with elastomeric bearings and three cases with three studied pedestals. Because of the large amount of resulting data, a statistical effects model is employed. The statistical effects model is a statistical tool that uses the statistics of the data to investigate the effect of each studied parameter such as bearing type, bridge location and hazard level on the structural responses. Results show that elevating bridges with the studied steel pedestals decreases longitudinal and transverse deck displacements, longitudinal shear and moment in columns, cap beam moment and pounding force. In the transverse direction, elevating the bridge leads to an increase in the abutment force. Also, results show that the studied tall steel pedestals are more effective than the studied short steel pedestal in decreasing longitudinal shear and moment in columns and decreasing transverse deck displacements while offering a height advantage. A study of the stability of the pedestals in this paper shows that the three types of studied pedestals may become unstable in earthquakes, thereby serving as a means to help determine where the installation of steel pedestals would not seem detrimental.     

Cyclic behavior of bolted connections with different arrangement of bolts

During the 1994 Northridge earthquake, relatively poor performance of the bolted web-welded flange connections (BWWFs) was observed. Thereafter, various types of connections such as end plate and T-stub bolted connections were suggested to be used in moment resisting frames that are often used in industrial and tall buildings. In this paper, finite element simulation is used to study and compare the cyclic behavior of fourteen specimens of the mentioned connection type by changing the horizontal and vertical arrangement of bolts. The results show that the moment capacity and the initial rotational stiffness of T-stub bolted connections are higher than that of end plate bolted connections designed based on AISC considering the total energy dissipation of both groups to be approximately equal. It is also evident that the probability of failure mode change in T-stub connections is higher than that of end plate connections under cyclic loading due to the arrangement variation of bolts. Based on the results of this paper, end plate connections are suggested for conditions where the imperfection in construction is probable.     

Continuous cadmium removal from aqueous solutions by seaweed in a packed-bed column under consecutive sorption-desorption cycles

Packed-bed column process efficiency for cadmium adsorption from aqueous solution was investigated under different bed heights (2.6 to 7.5 cm) and feed flow rates (15 to 30 ml min^?1). The column was filled with brown seaweed, Sargassum angustifolium. Three simplified models, including Bed Depth Service Time, Thomas, and Yoon-Nelson were employed for describing the experimental breakthrough curves as well as achieving design parameters. Bed lifetime was also evaluated in several consecutive sorption-desorption cycles. Cadmium concentration of 0.005mg l^?1, as a standard limit for potable water, was considered as the breakthrough concentration. The maximum column performance was achieved 81% at 7.5 cm bed length and flow rate of 15 ml min^?1. Indeed, increasing the bed height increased the sorption performance and service time, while increasing the feed flow rate had a negative effect. Maximum sorption capacity value remained almost constant by the bed height changes; however, increase in the feed flow rate slightly decreased it. The modeling results revealed that the Yoon-Nelson model was more accurate than Thomas for describing the experimental breakthrough data, especially at low flow rates. Column service time predictions were surprisingly achieved using the Bed Depth Service Time model even at extrapolations. 20% reduction in column adsorption efficiency was observed at the end of four consecutive sorption-desorption cycles; however, desorption efficiencies were achieved more than 99% in each cycle.     

Adsorption and photocatalytic degradation of organic dyes onto crystalline and amorphous hydroxyapatite: Optimization,kinetic and isotherm studies

We evaluated the adsorptive/photodegradation properties of hydroxyapatite. Hydroxyapatite was synthesized by two different precipitation methods and examined for the removal of two kinds of textile dye. The physicochemical properties of the products were characterized using Fourier transform infrared, X-ray diffraction, inductively coupled plasma atomic emission spectroscopy and scanning electron microscopy. The effects of different parameters, including hydroxyapatite synthesis method and removal process type, pH, reaction time, temperature and amount of hydroxyapatite, were investigated and optimized by Taguchi design. The kinetics of adsorption and isotherm studies showed that the pseudo-second-order model and the Freundlich isotherm were the best choices to describe the adsorptive behavior of hydroxyapatite. Photocatalytic degradation of dye followed Langmuir-Hinshelwood mechanism, illustrated a pseudo-first-order kinetic model with the adsorption equilibrium constant and kinetic rate constant of surface reaction equal to 0.011 (l mg^-1) and 1.3 (mg l ^-1 min^-1), respectively.     

Effects of Heat Treatment on Microstructural Modification of As-Cast Gamma-TiAl Alloy

Effects of normalizing and annealing treatments on the microstructure of Ti-48Al-2Cr-2Nb (at.%) were investigated. Normalizing processes were done at 1385 ± 5 °C in α-phase domain with the heating rate of 10 °C/min, the average cooling rate of 30 °C/min, and the holding times of 5, 10, 15, 20, and 25 min. The annealing process was done at the same temperature and heating rate, the holding time of 15 min, and the average cooling rate of 2 °C/min. Microstructures, phases, and hardness levels were studied by optical and field emission electron microscopic observations, x-ray diffractometry (XRD), and microhardness testing, respectively. Also, crystallographic texture variations were analyzed by means of texture coefficient and XRD results. Experimental results showed a linear direct relationship between treatment time and grain size, up to 15 min. A linear reversed behavior was observed for longer times. The untreated alloy consisted of γ and α₂ phases with a columnar morphology with the length of about 300 μm. A near-lamellar microstructure with equiaxed gamma grains, Widmansttäten, and laminar γ + α₂ colonies was obtained by the normalizing process. The maximum reduction of the grain size was about 70%, as achieved by normalizing with the 15 min holding time. A texture-free microstructure was acquired by normalizing treatment in comparison with strong texture of the as-cast and annealed alloys.     

Effect of milling time and clay content on the thermal stability of polyethylene‐clay nanocomposite

The aim of the paper was to investigate the thermal properties of polyethylene (PE)‐clay nanocomposites prepared via the high energy ball milling (HEBM) method. The structure and morphology of the nanocomposites were examined by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Thermal stability of all milled samples, including pure PE and PE‐clay nanocomposites was measured by thermal gravimetric analysis (TGA). The effect of milling time and clay contents on the thermal stability of PE was investigated. The results show that the thermal stability of PE promotes with increasing milling time. Clay has two opposed functions in the thermal stability of the nanocomposite, the first one is the barrier effect to improve the thermal stability, and another one is the catalysis effect leading to a decrease of the thermal stability. J. VINYL ADDIT. TECHNOL., 22:285–292, 2016. © 2014 Society of Plastics Engineers     

Different effects of process conditions on PA6/nanoclay composites at nanoclay contents above and below percolation threshold: Rheological,thermo‐dynamical,and thermal properties

The effects of several factors (i.e., nanoclay content (NC), melt temperature, screw speed, and feeding rate), on morphology, rheology, thermodynamics, and thermal stability of PA6/NC samples produced in a co‐rotating twin‐screw extruder were studied. We discuss how changes in the level of these factors can vary diffusion or imposed shear, how these variations in diffusion and/or shear can affect NC dispersion, and how the changes in the state of NC dispersion can influence several properties of the samples. Samples with low NC content, below percolation threshold, showed exfoliated/intercalated structure with negligible sensitivity to changes in the level of the factors; whereas, samples with high NC content, above percolation threshold, showed intercalated with sporadic flocculated structures and noticeable sensitivity to the changes in the level of the factors. Moreover, NC dispersion was found to be mostly diffusion‐controlled: changes that resulted in higher diffusion or residence time (i.e., high melt temperature or low screw speed) also eventuated in better NC dispersion. What is more, percolation threshold was seen to move to lower NC contents as diffusion rate was increased. Moreover, as NC content increased, opposite thermal stability behaviors were observed at above and below the percolation threshold. J. VINYL ADDIT. TECHNOL., 22:259–266, 2016. © 2014 Society of Plastics Engineers