Abstract: A heat resistant cast steel tube from an ammonia plant made of modified HP40 steel that failed after seven years of service was investigated for damage mechanism. The assessment of material degradation was carried out using optical microscopy, scanning electron microscopy (SEM) in combination with energy dispersive spectroscopy (EDS) analysis and mechanical tests. The main cause of failure appears to be overheating and localized corrosion along the network of intergranular carbides. Failed portion of the tube showed that the interdendritic eutectic carbides had coarsened, secondary carbides were precipitate and strongly coaresned within the austenitic regions. Witch decrease the mechanical strength and ductility of the service exposed tube compared with the as cast tube. Presence of unacceptable impurities like chlorine in the internal working gas destroy the protective oxide layer leading to penetration of corroding elements and degradation of service life of the tube.
Abstract: In the present work, Fe-Cu based alloys with different compositions have been obtained by using Powder metallurgy (PM). These alloys were created with the purpose of increasing mechanical properties of the parts. Nevertheless, little have been published, once this is a matter of industrial interest. In this work, samples of Fe100-x Cux (x=0.40, 0.55, 0.70, 0.85 and 1) alloys were processed by cold pressing at 10 MPa, followed by sintering at 1250 C°. Structures formed during sintering were studied by EDS. Microstructural aspects were observed by MEB. Densification and microhardness tests were also performed.
Abstract: In this work, we focus on a new generation of polymer named Polybutylene terephthalate (PBT). In order to analyse and determine true behaviour of this polymer, a special experimental method was used. Hence, the true stress/strain responses are investigated under a large plastic deformation in different stress triaxiality frameworks with a particular attention on the volumetric strain evolution, with their decomposition to an elastic volumetric strain, plastic volumetric strain and the pure shear. Moreover, the effect of stress triaxiality on the plastic instability and the fracture strain is also examined. With the plastic instability analysis, it was found that plastic strain hardening increases gradually with the triaxiality. Finally, in order to evaluate the damage of this polymer, a theoretical damage formula is proposed.
Abstract: This study aims at a better understanding of the behaviour of very high performance concretes (VHPC) subjected to high temperatures. The temperature increase within the concrete originating from the hydratation exothermic reaction of cement is emphasized by the mass effect of the structures and can lead to thermal variations of around 50°C between the heart and the structures walls. These thermal considerations are not without consequence on durability and the physical and mechanical properties of very high performance concrete, such as the compressive strength. This work is an experimental research that shows the effects of temperature on the mechanical properties of very high performance concrete (VHPC) and compares them with those of conventional concrete and HPC. Test specimens in usual concrete, HPC and VHPC are made, preserved till maturity of the concrete, and then subjected to a heating-cooling cycle from room temperature to 500°C at heating rate 0.1°C/min. Mechanical tests on the hot concrete and cooling (air and water) were realized. The results show that the mechanical characteristics of VHPC (density, compressive strength, tensile strength and elastic modulus) decrease with increasing temperature, but their strength remains higher than that of conventional concrete.
Abstract: Flexible pavements deteriorate and crack with time due to the frequent traffic load imposed upon it. Many studies have been done to predict the effects of frequent traffic load and environmental conditions on pavements in the effort to find the best pavement design which resist deterioration and ensure longer pavement service time. This study investigates the effect of mixing asphalt with varying percentages of nano calcium carbonate (CaCO3), namely 0, 2, 4, and 6 %. The mixtures were designed based on the Superpave mix design criteria. Investigation was done using several tests, namely resilient modulus, indirect tensile strength, moisture susceptibility, and dynamic modulus tests. Samples were subjected to aging to determine their resilient modulus. The results of the investigation show that resilient modulus and indirect tensile strength increased when higher percentages of nanoparticles were added to asphalt mixture, with improvement of 138 and 48.18% respectively. Modified binders showed up to 17% improvement in moisture susceptibility comparison to base asphalt mixture, while the result of dynamic modulus test showed that the stiffness of modified asphalt increased 76.69%. The investigation also found that adding 6% CaCO3 nanoparticles to asphalt produced modified asphalt with the best performance. In addition, the results show that the modified asphalt with CaCO3 is suitable for hot and humid regions (tropical countries) in the field of highways construction, as the modifier was able to mitigate the influences of high-temperature rutting and moisture damage.
Abstract: Much of the current research on concrete engineering has been focused on including siliceous additions as supplementary cementitious materials (SCMs). Silica reacts with Calcium hydroxide release during cement hydration, and produces more C-S-H. The latter contributes to increase compactness, mechanical strengths and sustainability of concrete. This paper explores the hydration characteristics of cement paste based on various natural mineral additions, that are very abundant in Algeria and present a high silica content (ground natural pozzolana “PZ” and ground dune sand “DS”). For this purpose, several analyses were carried out on modified cement pastes and mortars. These SCMs were introduced by replacement levels of 15, 20 and 25 by weight of cement. We first, studied the effect of these SCMs on the heat of hydration and mechanical strength of mortars at different ages. The evolution of hydration of modified paste was studied, by using Thermal analysis (TG/TDA) at different ages, to analyze the Calcium Hydroxide (CH) content of the modified pastes. It is shown that the CH content of the mixes including SCMs is lower than that of the plain cement paste, indicating that silica reacts with the cement paste through a pozzolanic reaction. Increased pozzolanic activity results in higher amounts of Calcium Silicate Hydrate in the paste, which in turn results in higher compressive strength for modified cement mortars. Due to its crystalline morphology, the ground DS particles present a partial pozzolanic effect, compared to PZ which is semi-crystalline. Modified mortars by 20% DS can be the optimal composition. It presents satisfactory results: good mechanical strength and low heat of hydration. It can lead to an economic and sustainable concrete. Ground DS is very abounded in Africa and free of any impurities and can be a good alternative SCMs in cement industry.
Abstract: The objective of this work is to evalute the coagulation-flocculation efficiency of the aluminum sulfate for the elimination of aromatic organic molecules (phenylalanine and catechol) in the presence of mineral salts of Ca2+ , SO42- and PO43-.Trials were conducted on the one hand on synthetic solutions of aromatic compounds in distilled water enriched by ions of calcium, sulphates and phosphate ions introduced in various forms (CaCl2 ; CaSO4 ; MgSO4 ; Na2SO4 ; NaH2PO4 ; KH2PO4), and on the other hand on Algerian drilling waters of different physicochemical characteristics. Results show that the addition of minerals salts seems to improve the yields of elimination of aromatic compounds tested and affects the optimal pH range of coagulation. The application of this process on mineralized waters (water drilling) leads to improve yields compared with those obtained in distilled water. It was also found that the process efficiency depends on the nature and the number of functional groups on the molecules and on their position relative to each other. The main mechanisms would be either a physical adsorption ,an exchange of ligand or a complexation on the floc surface of aluminum hydroxides.
Abstract: In this paper, Adaptive Neuro-Fuzzy Inference System (ANFIS) was used to model and predict Grewia Polysaccharide Gum (GPG) extraction yield from Grewia mollis (GM) powder/water system. The data for modelling the process behaviour consisted of four inputs (process temperature, GM powder/water ratio, process time and pH) and GPG yield as the output. The gbell Membership Function (MF) was used for the fuzzification of input variables and hybrid algorithm was chosen for the learning method of input–output data of the process. Simulation study was conducted on the developed ANFIS architecture at different MFs and epoch numbers to establish minimum error and maximum correlation coefficient (R) of the model. From the results obtained, ANFIS can be used as a reliable tool for modelling and prediction of GPG powder/water extraction process behaviour. The R between the experimental and predicted values was found to be high (> 0.96) and the mean percentage error was less than 2%, showing the great efficiency and reliability of the developed model.
Abstract: This study addresses the effective mitigation of power quality disturbance such as unbalanced voltage, voltage fluctuation, voltage variation of secondary distribution network using dynamic voltage restorer (DVR). To make distribution system operate at its best performance and minimum loss, DVR is employed. The proposed system is designed using MATLAB/Simulink in Sim Power System tool box. Considering, nevertheless, that standard acceptable performance implies correct voltage profile, minimum loss, no phase shift for voltage and current, absence of overloading of transformers and electrical wires, and acceptable frequency deviation. The new setup of DVR has been put forward using dq0 controller and proportional integral (PI) controller method to improve voltage profile, correct unbalance voltage and enhance power quality problems in secondary distribution network. The simulation results attest to the ability of the proposed DVR configuration in mitigating the power quality problems in secondary distribution network.
Abstract: Marine communication and navigation technologies go hand-in-hand in order to provide a safe and secure marine travel on those who are on board a vessel or a ship. These tools are used together to establish rapport between sea ports and nearby vessels, as well as determining a sea or ocean’s characteristics and weather patterns. Unmanned Surface Vehicle (USV) for maritime salvage is designed to mitigate the menaces associated with marine navigation. The technique involves intelligent navigation and communication, intelligent collision avoidance and intelligent rheostat systems. This paper seeks to explore the technological advancements in marine communication and navigation used in the maritime environment, with veneration to both hardware and software. This review would invariable serve as a source of information pool for further studies. We also present some current technological challenges the marine industry is antagonized with.