Composites realized by hand lay-up process in a civil engineering environment: initial properties and durability

The repair, the reinforcement as well as the setting in safety of buildings and existing reinforced and/or pre-stressed concrete structure is a real technological stake and a socio-economic problem for the near future. The introduction of composites in civil engineering is an interesting answer to these goals, but they brought an important amount of new problems that have to be solved for safe structural applications under combined mechanical and environmental loadings. In fact during the past five years, we have witnessed exponential growth in research or field demonstrations of fiber-reinforced composites in civil engineering. Manufacturers and designers have now access to a wide range of composite materials. However, they face great problems with forecasting the reliability of composite materials. Their introduction in civil engineering applications is a difficult operation due to working environment and weathering conditions. The objective of this paper is to study the effect of these conditions and their consequences on the mechanical properties of the final composite. An analysis of the rheological (viscoelastic) properties was carried out in order to observe the glass transition temperature evolution according to reactive mixture stoichiometry and weathering conditions.     

Ageing of carbon/epoxy and carbon/vinylester composites used in the reinforcement and/or the repair of civil engineering structures

This paper presents an experimental approach to study the durability of FRP composites used in the civil/structural engineering. Carbon epoxy (carbon/EP) and carbon vinylester (carbon/VE) composites were considered for accelerated ageing (thermal, hygrometric, chemical, thermochemical, hydrothermal, freezing–thawing cycles, etc.) over 18 months. The accelerated ageing tests were selected to reflect the real operating conditions on natural civil engineering environment. The same composites were also subjected to environmental ageing to assess the effectiveness and the relevance of the accelerated exposure. Changes in tensile strength and viscoelastic response were evaluated through mechanical testing and Kinemat analysis. The design factors prescribed by the existing principle guidelines were applied to experimental measurements. The results revealed the presence of drawbacks inherent in these regulations based on a determinist approach.     

A New PWM Strategy Based on a 24-Sector Vector Space Decomposition for a Six-Phase VSI-Fed Dual Stator Induction Motor

This paper presents a new space vector pulsewidth modulation (SVPWM) technique for the control of a six-phase voltage source inverter (VSI)-fed dual stator induction machines (DSIM). A DSIM is an induction machine which has two sets of three-phase stator windings spatially shifted by 30 electrical degrees and fed by two three-phase VSIs. Despite their advantage of power segmentation, these machines are characterized by large zero sequence harmonic currents, and in particular those of order 6 k plusmn 1, which are due to the mutual cancellation between the two stator windings. The proposed SVPWM scheme, while easy to implement digitally, reduces significantly these extra stator harmonic currents. Experimental results, collected from a 15 kW prototype machine controlled by a digital signal processor, are presented and discussed.     

Repair and Restoration of the Optical Properties of Sandblasted Glasses By Silica-Based Sol-Gel Coatings

The damage provoked by sand storms in Sahara desert to windscreen of vehicles and solar mirrors is a problem. Different solutions have been proposed, one of them is the application of polymeric coatings, but they rapidly degrade. In this work, we have deposited silica-based sol-gel coatings including silica nanoparticles onto sandblasted glasses. The glasses were eroded by sandblasting varying the projected sand mass and the incidence angle to obtain different surface states. The eroded samples were coated by dipping with a silica layer to correct the defects induced by sandblasting and restore the optical transmission. The damage increases with increasing projected mass and the impact angle. The optical transmission decreases with increasing damage. In extreme conditions, optical transmission falls from 91.5% to 68.6%. The deposition of silica-based layers containing SiO₂ colloidal nanoparticles promotes the repairing of sandblasting defects. A strong decrease of roughness to values similar to those of as-received glass is related with the increasing of the optical transmission up to levels permitting of windscreens and solar mirrors. Transmittance measurements showed a remarkable improvement in all cases, whatever the projected sand mass or the impact angle. For highly degraded samples, the transmission increases from 68.6% to 91.4%, an improvement of near 23%.     

Hybrid Cascaded H-Bridge Multilevel-Inverter Induction-Motor-Drive Direct Torque Control for Automotive Applications

This paper presents a hybrid cascaded H-bridge multilevel motor drive direct torque control (DTC) scheme for electric vehicles (EVs) or hybrid EVs. The control method is based on DTC operating principles. The stator voltage vector reference is computed from the stator flux and torque errors imposed by the flux and torque controllers. This voltage reference is then generated using a hybrid cascaded H-bridge multilevel inverter, where each phase of the inverter can be implemented using a dc source, which would be available from fuel cells, batteries, or ultracapacitors. This inverter provides nearly sinusoidal voltages with very low distortion, even without filtering, using fewer switching devices. In addition, the multilevel inverter can generate a high and fixed switching frequency output voltage with fewer switching losses, since only the small power cells of the inverter operate at a high switching rate. Therefore, a high performance and also efficient torque and flux controllers are obtained, enabling a DTC solution for multilevel-inverter-powered motor drives.      

Wind Turbine Efficiency Under Altitude Consideration Using an Improved Particle Swarm Framework

In this work, the concepts of particle swarm optimization-based method, named non-Gaussian improved particle swarm optimization for minimizing the cost of energy (COE) of wind turbines (WTs) on high-altitude sites are introduced. Since the COE depends on site specification constants and initialized parameters of wind turbine, the focus was on the design optimization of rotor radius, hub height and rated power. Based on literature, the COE is converted to the Saudi Arabia context. Thus, the constrained wind turbine optimization problem is developed. Then, non-Gaussian improved particle swarm optimization is provided and compared with the conventional particle swarm optimization for solving the optimization design in wind turbine efficiency under different altitudes ranging from 2500 to 4000 m. The results show that as altitude rises, the optimal rotor radius grows, but the optimal hub height and rated power drop, resulting in an increase in COE. Further, the non-Gaussian method display a faster convergence compared to the classical particle swarm optimization. These findings will be useful as a reference for wind turbine design at high altitudes. Thus, it could be employed to optimize the initialized parameter of wind turbine for the planned and largest wind farm in Saudi Arabia in Dumat Al-Jandal selected site.

     

Aging Effects of Epoxy Resin on Joining of Aluminum Plates

Aluminum plates (type 2024) were subjected to various surface pretreatments and then joined by epoxy resin. The joints were tested for shear strength close to the time of joining, and after various storage periods at 25±5°C and 40% relative humidity. Surfaces of the aluminum plates were examined using X-ray photoelectron spectroscopy, and scanning electron and optical microscopies. Specimens examined shortly after being joined showed a trend of cohesive failure, but those which were stored for some time showed a trend of adhesive failure. It was found that the mean shear strength (MSS) of the specimens treated by a chromic acid solution was lower than that of specimens treated by a phosphoric acid solution. Hardness (Shore type D-2) and structure (by X-ray diffraction) of epoxy control samples were also examined. It was observed that the hardness increases with longer aging time, while changes in the structure were observed after long-term storage (63 months). The failure development with time is discussed and correlated with the MSS and the failure mode.     

Removal improvement of bacteria (Escherichia coli and enterococci) in maturation ponds using baffles

Korba wastewater treatment plant is a conventional activated sludge followed by three maturation ponds (MP1, MP2, MP3) in series acting as a tertiary treatment. The first study of wastewater treatment plants showed that the effluent concentration of Escherichia coli and enterococci at the outlet of the (MP3) varies between 10(3) and 10(4)CFU/100 ml. After the hydrodynamic study conducted by Rhodamine WT which showed short-circuiting in the MP1, two baffles were introduced in the first maturation pond (MP1) to improve the hydrodynamic and the sanitary performances. The second hydraulic study showed that the dispersion number 'd' was reduced from 1.45 to 0.43 by this engineering intervention and the Peclet number was raised from 0.69 to 2.32. The hydraulic retention time was increased by 14 h. Because of well-designed baffles, the removal efficiency of E. coli and enterococci was raised between 0.2 and 0.7 log units for the first maturation pond.     

Optimizing the heat sealing parameters of multilayers polymeric films

Polymer–metal multilayers have been widely used for decades in packaging industry, and more recently for vacuum insulation panels for building application. In both cases, the seal zone could represent a weak area for mechanical and barrier properties. The aim of this report is to investigate the heat sealing properties of multilayers composed of one polyethylene layer and one or three polyethylene terephthalate layers coated with aluminum. The quality of seal was quantified by peeling test and the failure mechanisms. In order to optimize the set of heat sealing parameters, a series of mechanical and morphological relevant parameters were measured and compared to the failure modes. A comparison between the sole sealant film and multilayers was performed in terms of range of optimal heat sealing parameters and mechanical behavior of seals. Although they present a much narrower range of optimal properties, the multilayers films show a strong advantage over the single films.