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[en] Fibre-reinforced concrete (FRC) allows reduction in, or substitution of, steel-bars to reinforce concrete and led to the commonly named structural FRC, with steel fibres being the most widespread. Macro-polymer fibres are an alternative to steel fibres, being the main benefits: chemical stability and lower weight for analogous residual strengths of polyolefin-fibre-reinforced concrete (PFRC). Furthermore, polyolefin fibres offer additional advantages such as safe-handling, low pump-wear, light weight in transport and storage, and an absence of corrosion. Other studies have also revealed environmental benefits. After 30 years of research and practice, there remains a need to review the opportunities that such a type of fibre may provide for structural FRC. This study seeks to show the advances and future challenges of use of these polyolefin fibres and summarise the main properties obtained in both fresh and hardened states of PFRC, focussing on the residual strengths obtained from flexural tensile tests.
[es]El hormigón reforzado con fibras (HRF) permite la reducción parcial o total de barras de acero en el hormigón armado, acuñándose término HRF estructural, siendo las fibras de acero las más usadas. Las macro-fibras poliméricas son una alternativa a las de acero, aportando estabilidad química y menor peso para resistencias residuales iguales. Además, las fibras de poliolefina ofrecen beneficios adicionales tales como mayor seguridad de trabajo, menor desgaste de equipos de bombeo, menor peso en el transporte y almacenamiento, y ausencia de corrosión. Otros estudios también han revelado beneficios medio-ambientales. Después de 30 años de investigación y práctica, sigue siendo necesario analizar las oportunidades que estas fibras de poliolefina pueden proporcionar al HRF estructural. Este estudio muestra los avances y posibilidades del uso de estas fibras y resume las principales propiedades obtenidas tanto en estado fresco como endurecido, centrándose en la resistencia residual obtenida en los ensayos de tracción por flexión.
[en] Thermomechanically controlled processed steels have gained attention increasingly by many industries. In this research S700MC steel is successfully welded using low power pulsed Nd:YAG laser and the microstructure and mechanical properties are investigated. It is shown that the average power and overlapping factor both affect the weld geometry. Full penetration with double-sided welding achieved on 2 mm thick plates autogenously. Optical metallographic methods and SEM/EDS were used to evaluate the resulting microstructures. The evaluations revealed that the weld metal microstructure contains different morphologies of ferrite such as acicular, allotriomorphic and Widmanstätten as well as bainaite and martensite structure in the weld zone. Also, no noticeable heat affected zone was detected near the fusion zone of the weldments. In addition to microstructures investigation, micro hardness and tensile tests were performed to evaluate mechanical properties. Hardness measurement results exhibit higher hardness values in weld zone than that of in the base metal. The tensile test revealed a ductile fracture behavior which happened in the base metal, due to proper weld zone microstructure. The strength and elongation of the prepared joints were 774 ± 14 MPa and 26.5 ± 2.5%, respectively. (author)
[en] The experimental study was conducted on rheological properties in laboratory to measure the integrity of cement slurry. Three samples were used and analyzed at different parameters to check the elasticity of cement slurry. Additives with various concentrations, i.e. silica fume % BWOC (Present by Weight on Cement) (15, 17, 19 and 21), dispersant % Wt (Percent Weight) (0.21, 0.26 and 0.31) and additional 1; % Wt of fluid loss control were used to improve the performance of the cement slurry at the temperature of 123 degree C. The results have shown that increase in the concentration of dispersants that have caused to decrease in the Plastic Viscosity (PV), Yield Point (YP) and GS (Gel Strength). The rheological properties of cement were improved with the addition of fluid loss control additive in 21 % BWOC (Present by Weight on Cement) silica fume increase the water quantity in cement slurry that improve its durability and to reduce the strength retrogression in High Temperature High Pressure (HTHP) environment. Results were achieved through HTHP OFITE Viscometer (Model 1100). (author)
[en] The effect of sub-zero treatments on dry sliding wear performance of Vanadis 6 tool steel was investigated by pin-on-disc tests against three counterpart types: alumina, 100Cr6 ball bearing steel, and CuSn6 bronze. The microstructure of the examined steel consists of tempered martensitic matrix with very small amounts of retained austenite, and three carbide types. Sub-zero treatments increase the carbides count. The hardness of the steel increases with increasing the austenitizing temperature but slightly decreases with the application of sub-zero treatments. Sub-zero treatments affect the wear performance of the Vanadis 6 steel when tempered at the secondary hardening peak as follows: almost no effect of this kind of treatment was detected when alumina was used as a counterpart but moderate amelioration was recorded when either 100Cr6 steel or CuSn6 bronze was used in the sliding couple. This behaviour is attributed to the combined effect of hardness variations and changes in population density of carbides, due to application of sub-zero treatment.
[en] In this work, we have attempted to prepare a comparative machinability study of wire electrical discharge machining of different difficult-to-machine materials, viz., stainless steel (SS) 316, H21 hot work tool steel and M42 highspeedsteel (HSS). The key features, which are compared during the analysis, are mainly material removal rate, average surface roughness, kerf width, wire consumption rate (WCR), recast layer (RL), elemental diffusion, surface morphology and micro-hardness of the machined surface. They are found to be greatly influenced by pulse energy. The pulse energy is calculated in terms of ‘specific discharge energy’. Apart from the discharge energy, the thermal conductivity of the material also plays an important role in the formation of RL and inclusion of foreign elements such as carbon, oxygen, copper and zinc in RL. H21 steel has been found to be more prone to thermal defects due to its high-thermal conductivity and high tensile residual stresses, whereas more re-solidification of foreign materials is observed in SS316 and M42 HSS due to their high adhesive properties and low-thermal conductivity. But, in low-energy cutting, more uniform surfaces are observed in H21 steel in comparison with other two types of steel. (author)
[en] Carbonation is a deleterious concrete durability problem which may alter concrete microstructure and yield initiation of corrosion in reinforcing steel bars. Previous studies focused on the use of Artificial Neural Networks (ANN) for the prediction of concrete carbonation depth and to minimize the need for destructive and elaborated civil engineering laboratory tests. This study aims to provide improved accuracy of simulation and prediction of carbonation with an ANN architecture including eighteen input parameters employing alternative Scaled Conjugate Gradient (SCG) function. After ensuring a promising value of the coefficient of correlation as high as 0.98, the influence of proposed input parameters on the progress of carbonation depth was studied. The results of this parametric analysis were observed to successfully comply with the conventional civil engineering experience. Hence, the employed ANN model can be used as an efficient tool to study in detail and to provide insights into the carbonation problem in concrete.
[es]La carbonatación es un problema perjudicial de durabilidad del hormigón que puede alterar la microestructura del hormigón y provocar el inicio de la corrosión en barras de refuerzo. Estudios previos se centraron en el uso de redes neuronales artificiales (RNA) para la predicción de la profundidad de la carbonatación del hormigón y para minimizar la necesidad de pruebas de laboratorio destructivas y elaboradas. Este estudio tiene como objetivo proporcionar una precisión mejorada de la simulación y la predicción de la carbonatación con una arquitectura RNA que incluye dieciocho parámetros de entrada con una función alternativa de Gradiente de Conjugado Escalado. Después de asegurar un valor prometedor del coeficiente de correlación tan alto como 0.98, se estudió la influencia de los parámetros de entrada propuestos en el progreso de la profundidad de carbonatación. Se observó que los resultados de este análisis paramétrico cumplían exitosamente con la experiencia de ingeniería civil convencional. Por lo tanto, el modelo RNA empleado puede ser utilizado como una herramienta eficiente para estudiar en detalle y proporcionar información sobre el problema de carbonatación en el hormigón.
[en] The applications of the interval and standard probabilistic approaches for verifying the reliability of the results of an experiment studying the mechanical properties of nuclear materials are compared. The presence of “outliers” in a sample of hardness values for hafnium ingots is studied with for fixed oxygen mass content. The situation of measurement error limitation without reliable information about its distribution is considered. The correctness of the application of numerical methods of interval analysis for processing experimental data under conditions of uncertainty and noisy experimental data is shown. (author)
[en] The Cold Worked and Stress Relieved (CWSR) Zr-2.5Nb pressure tube material exhibits both microstructural and crystallographic anisotropy. In order to delineate both the effects, CWSR Zr-2.5Nb PT material was imparted suitable heat-treatments. The hardness and Young’s Modulus of as-received as well as heat-treated PT material were determined along three orthogonal directions with respect to the tube using nano-indentation technique. The variation of grain morphology and texture were investigated in all three orthogonal directions for the as received and heat treated samples using SEM and EBSD. An attempt has been made to quantify the microstructural and crystallographic contribution to anisotropy in hardness. (author)
[en] An exhaustive study of the erosion process of a copper cathode exposed to a hot plasma column of 2kJ of energy (T≈0.5-2.0keV) and high electron density (n≈1019-1022cm3) was made, as well as, the radiation field of charged and neutral particles. The characterization of the cumulative damage generated by the plasma/cathode interaction was made by the use of metallographic techniques, scanning electron microscopy (SEM) and by the analysis of mechanical properties. Damage accumulation produced by the impacts of deuterium plasma discharge created in the copper electrode a deep cavity similar to a crater, modifying the morphology of the surface and below it. The microhardness Vickers test was carried out making indentations from the final part of the cavity to cover 1 cm with indentations every 200 μm. Different areas of hardening were observed, the profile suggests a hardening/recovery front and simultaneous recrystallization in the sample, phenomenon associated with the heating/cooling cycles to which the copper cathode is subjected. Images were captured by SEM at different distances from the center of the surface. The region that showed involvement at the macro level corresponds to 2/3 of the radius of the sample from the center to the outside. These phenomena studied are important to understand the nature of the plasma/wall interaction in any fusion device. (author)
[en] (CuxAg1−x)7SiS5I mixed crystals were grown by the Bridgman–Stockbarger method. The microhardness measurements are carried out at room temperature using a Vickers indenter. The compositional dependence of the microhardness is studied. The dependence of the microhardness on the depth of imprint is analyzed in the model of geometrically necessary dislocations. The indentation size effect is observed. It is established that the microhardness of (CuxAg1-x)7SiS5I mixed crystals decreases at the substitution of Cu atoms by Ag atoms. (author)