Deesy G. Pinto

Oxide Inclusions in Steel Welds of Car Body

The goal of this research is to choose the proper method of car body welding. Properties of weld metal deposits depend on many conditions. First of all, this paper attempts to study the role of oxide inclusion sites on the transformation of austenite to acicular ferrite in steel weld metal deposits and their toughness. Safety and exploitation conditions of welded steel structure depend on many factors. The most significant of those factors are connected with materials, welding technology, state of stress and temperature. Because of that a good selection of steel and welding method is crucial to obtain proper steel structure. Car body elements of higher durability are made of low carbon and low alloy steel, very often with small amount of carbon and the amount of alloy elements such as Ni, Mn, Mo, Cr and V in low alloy steel and their welds. In the terms of the kind of steel it is used a proper welding method and adequate filler materials. In the present paper the influence of Mn, Ni, Mo, in WMD on the behaviour of steel structure for low temperature service was tested.

Mechanical Properties of Epoxy Nanocomposites Using Alumina as Reinforcement - A Review

Polymers and their composites find use in many engineering applications as alternative products to metal-based ones and, nowadays, have wide technical applications. One of the most used composite materials is the epoxy resins (EP), which is a thermoset polymer matrix. After cure, this material displays some excellent mechanical, thermal, electrical and chemical properties. For these reasons, it has been widely used for a wide range of automotive and aerospace applications, as well as for shipbuilding or electronic devices. However, EP has poor resistance to crack propagation and is brittle. So, in recent years, a considerable amount of research has been carried out to improve the performance of the toughness of EP. The most common studied technique consist to reinforce the EP matrix with rigid nanoparticle fillers, such as alumina, silica, mica, talc, organoclays, nanoclays, carbon nanotubes, TiO2, among others. Among these nanofillers type, nanosize alumina particles has not been widely studied. However, recent studies have reported that the use of functionalized nanosize alumina particles as nanofiller can significantly improve the properties of the nanocomposite, even with low contents. These results, combined with the low cost of the alumina, show that the reinforcement of EP with alumina nanoparticles is a viable solution. In this paper, an attempt is made to review and highlight some recent findings and also some trends to show future directions and opportunities for the development of polymer nanocomposites reinforced with alumina nanoparticles.

Influence of Surface Area on the Flowability Behaviour of Self-Flow Refractory Castables

Alumina, with high melting point (2050°C), high hardness and mechanical strength, and excellent abrasion resistance, is one of the most common raw materials used in self-flow refractory castables (SFRC) for monolithic linings and is commercially available in various fine to coarse size classes. However, the performance of the refractory lining depends not only on the properties of its ingredients but also on its easy installation (good flowability). The aim of this work was to evaluate the relationship between the flowability index (FI) of fresh castable and the specific surface area (SSA) of its particles, which is mostly determined by the finer particles content. The results obtained showed that, by controlling the proportion between matrix and aggregate, it is possible to control the SSA of the refractory castable and find a mathematical relationship between the specific surface area and the minimum flowability index required to obtain a self-flow refractory castable. It is, thus, possible to optimize the refractory castable size composition and obtain an estimate for FI as a function of SSA. Using a minimum 45 wt.% matrix content in the castable mixture, a SSA value above 2.215 m2/g is obtained, which leads to FI ≥ 80%, the recommended value for self-flow.

Mechanical Properties of Alumina Nanofilled Polymeric Composites Cured with DDSA and MNA

Reinforced concrete is widely used in structures. New materials to replace both the steel and the concrete have been studied in many research centres. One of the possibilities for the reinforcement is the partial or total replacement of the steel bars by new composite materials. Nano composites are very promising, and an investigation line was developed to this end by an interdisciplinary team. On this work, the mechanical properties of epoxy resin nanocomposites (EPNCs) filled with α-Al2O3 nanoparticles (NPs) with irregular shape and approximately 100 nm maximum diameter size was investigated. The variable study was the alumina NPs contents: 1, 3 and 5 wt.%. The NPs were previously pretreated with a silane agent (APTES). Two hardeners, 3-dodec-2-enyloxolane-2,5-dione (DDSA) and 8-methyl-3a,4,7,7a-tetrahydro-4,7-methano-2-benzofuran-1,3-dione (MNA), frequently used in epoxy resin embedding tissues, were used simultaneously for this study. Unlike other hardeners, DDSA does not need curing treatment, constituting a novel application and a saving time-energy during the manufacturing process. Considering the mechanical behaviour, it was observed that the EPNCs filled with 5 wt.% of alumina NPs showed the maximum improvement in flexural modulus, around 14 % when compared to the pristine EP sample. No relevant effect was observed on the flexural strength by adding alumina NPs. Additionally, the maximum increase observed for hardness, and Young’s modulus were about 13 % and 28 %, respectively (the maximum increase was observed at 3 wt.%).

Influence of Transversal Reinforcement on Plastic Rotation Capacity of High-Strength Beams

This paper describes how the increase in knowledge about the potential of mixtures containing chemicals and mineral materials leads to the high-performance concretes, including high-strength concrete (HSC) in the last decade. When high strength, durability, and elevated service behavior are necessities high-strength concrete can be an economical solution. In general, it is known that increasing the compressive concrete strength leads to the deformability reduction resulting in a more brittle concrete. On the other hand, the low deformability of HSC doesn’t mean low deformability of the high-strength beams, because their behavior comes from a combined effect of concrete and reinforcement. One of the usual reinforcement elements is the stirrups (transversal reinforcement). By ensuring a sufficient concrete confinement in the compressive zone, and by its distribution along the beam length, this reinforcement can improve the plastic rotation capacity on the beam critical sections. This paper presents an experimental study about the influence of transversal reinforcement (stirrups) on the flexure plastic rotation capacity of high-strength beams. Flexural tests on five simply supported beams were carried out using a four-point bending load untill the failure load. The load position was favorable to create a central zone on the beam theoretically of pure flexure behavior without shear stress influence. The beams failures were governed by the pure flexure in the middle zone of the beams. In this study, only one solution of stirrups was used, corresponding to a transversal reinforcement ratio of 0.295%. The compressive concrete strength was between 75.0 and 90.6 MPa. The longitudinal reinforcement ratio was between 2.2 to 3.5%. The plastic rotation capacity in flexure is characterized by the use and definition of a plastic trend parameter. From the results of this study, a well-known positive effect on plastic rotation capacity caused by confinement with transversal reinforcement was shown. A bilinear law can induce the increment of plastic rotation capacity. This law states that the increment of plastic rotation capacity decreases in a large way as the longitudinal tensile reinforcement ratio increases, and becomes equal to zero from longitudinal reinforcement ratio 3.0 to 3.5%.