Creep analysis of bolted flange joints

In the petrochemical and nuclear industries, the difficulty in assessing the effect of creep on the tightening load of bolted flanged connections is recognized. Under high temperatures, the leak tightness of bolted joints is compromised due to the loss of the bolt load as a result of creep of not only the gasket and bolt materials but also the flange material. Apart from acknowledgment of this effect, there exists no established design calculation procedure that accounts for creep. This is because the relaxation of the bolt load and the corresponding loss of the gasket contact stress are not easy to assess analytically. The main objective of the work is the development of a simple analytical solution to the creep-relaxation problem encountered in bolted flange connections of the float type. Particular emphasis is put towards relaxation caused by the flange and bolt material creep.     

Heavy metal removal from aqueous solutions by activated phosphate rock

The use of natural adsorbent such as phosphate rock to replace expensive imported synthetic adsorbent is particularly appropriate for developing countries such as Tunisia. In this study, the removal characteristics of lead, cadmium, copper and zinc ions from aqueous solution by activated phosphate rock were investigated under various operating variables like contact time, solution pH, initial metal concentration and temperature. The kinetic and the sorption process of these metal ions were compared for phosphate rock (PR) and activated phosphate rock (APR). To accomplish this objective we have: (a) characterized both (PR) and (APR) using different techniques (XRD, IR) and analyses (EDAX, BET-N(2)); and, (b) qualified and quantified the interaction of Pb(2+), Cd(2+), Cu(2+) and Zn(2+) with these sorbents through batch experiments. Initial uptake of these metal ions increases with time up to 1h for (PR) and 2h for (APR), after then, it reaches equilibrium. The maximum sorption obtained for (PR) and (APR) is between pH 2 and 3 for Pb(2+) and 4 and 6 for Cd(2+), Cu(2+) and Zn(2+). The effect of temperature has been carried out at 10, 20 and 40 degrees C. The data obtained from sorption isotherms of metal ions at different temperatures fit to linear form of Langmuir sorption equation. The heat of sorption (DeltaH degrees), free energy (DeltaG degrees) and change in entropy (DeltaS degrees) were calculated. They show that sorption of Pb(2+), Cd(2+), Cu(2+) and Zn(2+) on (PR) and (APR) an endothermic process. These findings are significant for future using of (APR) for the removal of heavy metal ions from wastewater under realistic competitive conditions in terms of initial heavy metals, concentrations and pH.     

Evaluation of performance characteristics of the heavy vehicle simulator in Florida

The Florida Department of Transportation (FDOT) Materials Office has recently acquired a heavy vehicle simulator (HVS) and constructed an accelerated pavement testing (APT) facility which uses this HVS. An investigation was conducted to evaluate the operational performance of the HVS, and to determine its most effective test configurations for use in evaluating the rutting performance of pavement materials and/or designs under typical Florida traffic and climate conditions. Five trial runs with the HVS used a super single tire with a load of 4082 kg, tire pressure of 793 kPa and a wheel traveling speed of 12.9 km/h. These five trial runs used different combinations of wheel traveling direction (uni-directional or bi-directional), total wheel wander and wander increments. The uni-directional loading was found to be a more efficient mode for evaluation of rutting performance using the HVS. As compared with the bi-directional loading mode, the uni-directional mode produced substantially higher rut depths for the same number of wheel passes and also for the same testing time duration. When the bi-directional loading with no wander was used, imprints of the tire treads were observed on the wheel track. It was found that using a loading mode with wander smoothened out the imprints of the tire treads considerably. The uni-directional loading mode with 10 cm wander using 2.5 cm increments was selected to be used for evaluation of rutting performance based on consideration of testing efficiency and realistic rutting results.     

Optimum pumping scheme of dual-stage triple-pass erbium-doped fiber amplifier

The optimization of pump power for a new configuration of dual-stage triple-pass Erbium-doped fiber amplifier is successfully demonstrated. This configuration incorporates two-stage amplifiers with two independent 980-nm pump lasers. The first-stage amplifier consists of double-pass amplification to obtain high gains and the second-stage amplifier is single-pass amplification in backward pumping schemes. The maximum gain that obtained in the experiment does not have the minimum noise figure. Therefore, the optimum operating point is defined based on the ratio of gain to noise figure. The relationship between the pump-power distributions in the proposed configuration shows that the optimum pump ratio of the first-stage pump laser to the total pump power is around 0.3 to 0.5 depending on the signal powers.     

Phosphorus removal from aqueous solution using iron coated natural and engineered sorbents

New filtration materials covered with metallic oxides are good adsorbents for both cation and anion forms of pollutants. Sfax is one of the most important industrial towns in Tunisia. Its phosphate manufacture in particular is causing considerable amounts of water pollution. Therefore, there is a need to find out a new way of getting rid of this excessive phosphate from water. This work is aimed to examining the potential of three sorbent materials (synthetic iron oxide coated sand (SCS), naturally iron oxide coated sand (NCS) and iron oxide coated crushed brick (CB)) for removing phosphate ions from aqueous solutions. According to our literature survey CB was not used as adsorbent previously. Phosphate ions are used here as species model for the elimination of other similar pollutants (arsenates, antimonates). Optical microscope and scanning electron microscope (SEM) analyses were used to investigate the surface properties and morphology of the coated sorbents. Infra-red spectroscopy and X-ray diffraction techniques were also used to characterize the sorbent structures. Results showed that iron coated crushed brick possess more micro pores and a higher surface area owing to its clay nature. The comparative sorption of PO4(3-) from aqueous solutions by SCS, CB and NCS was investigated by batch experiments. The estimated optimum pH of phosphate ion retention for the considered sorbents was 5. The equilibrium data were analysed using the Langmuir and Freundlich isotherms. The sorption capacities of PO(4)3- at pH 5 were 1.5 mg/g for SCS, 1.8 mg/g for CB and 0.88 mg/g for NCS. The effect of temperature on sorption phenomenon was also investigated. The results indicated that adsorption is an endothermic process for phosphate ions removal. This study demonstrates that all the considered sorbents can be used as an alternative emerging technology for water treatment without any side effect or treatment process alteration.     

Influence of the rubber content and particle morphology on the mechanical properties of the (hiPP)

The effect of the final morphology and the role of ethylene propylene rubber (EPR) content and (iPP) particle size on the mechanical properties of (iPP/EPR) in situ blends are investigated. The addition of EPR causes a significant improvement in the impact strength of the composites, from 20 kJ/m² in unthoughned composite iPP to 100 kJ/m² in iPP/EPR composites containing 50% EPR. Conversely, the tensile strength and the Young's modulus of the blends decrease as the EPR amount increases. The mechanical tensile strength is similar for the composite which have a time of homopolymerization less or equal to 60 min, and a higher value is observed in the case of 100 min. The scanning electron microscopy characterization shows that the larger the iPP particle is, the less the rubber settles on the surface of the high impact polypropylene and the less the final material is resistant to shocks. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44197.     

Thermomechanical approach for the modeling of oblique machining with a single cutting edge

This article aims to predict performances of oblique machining with a single cutting edge. A thermomechanical approach for the modeling of oblique cutting with a single cutting edge is proposed. A good agreement was found between predicted and experimental data. New rules were established to determine experimentally the average friction coefficient and chip flow angle at the rake face. The computation algorithm permits to predict all thermomechanical parameters such as cutting forces, cutting temperatures, and chip geometry. Besides, all predicted oblique machining parameters are mainly controlled by the Po-criterion, which is defined as the ratio of tool–chip contact length to uncut chip thickness.     

Modelling of tolerances and manufacturing dimensions

To obtain imposed dimensional and geometrical specifications for any mechanical piece, production tolerances must be calculated. So a simulation of workpiece behavior when it is machined, has permitted calculations of deviations on machined surfaces.The method of deviation calculation is based on a comparison between imposed functional tolerance and the tolerance calculated in relation to deviations on two machined surfaces or between a machined surface and the operational datum.The one direction modelling of deviations inquires practical inputs such as the planning process, the operational datum, the deviations on rough surfaces, and deviations on surface datum for any stage of machining. The developed method allows determining the deviations on machined surfaces. Then, tolerances on production dimensions were calculated in three directions. These results have permitted to define average production dimensions, which may be used for NC machine programming and to prepare an optimal rough piece configuration.The developed method has been applied for the machining of a fixing screw.     

Electrical parameters degradation law of MOSFET during ageing

A new method to extract the different electrical parameters lifetime of MOS transistors submitted to hot carriers degradation is proposed. This method leads to error on the lifetime below 15%, even if the parameter variation measurement reaches only 8%. The robustness of this method has been tested for various biases of stress and different technologies representative of different ageing mechanisms. Finally this method is a good indicator of the degradation modes occurring during the stress.     

Contribution to the comprehension of dissipation phenomena in lead zirconate titanate: aliovalent doping effect

By the solid reaction method, undoped, potassium doped and niobium doped lead zirconate titanate (PZT) are elaborated. The mechanical losses measured in the range of the Hz as a function of temperature shows two peaks R₁ and R₂, and a ferroelectric transition peak P₁ between ferroelectric and para-electric states on the undoped PZT—Pb(Zr_0.54Ti_0.46)O₃—noted PZT54/46. Potassium doped PZT—Pb_1−xK_x(Zr_0.54Ti_0.46)O₃—shortly called PKZT 100x/54/46 shows an increase in the height of both the peaks at a doping content, x, less than 0.5 at.% but an opposite effect is observed above this value. Niobium doped PZT—Pb[(Zr_0.54Ti_0.46)_1−yNb_y]O₃—shortly called PNZT 100y/54/46, shows the vanish of the R₂ peak and the decrease of the height of the R₁ peak when the doping content increases.