Browsing by Author "Pereira, A. B."
Now showing 1 - 6 of 6
Results Per Page
Sort Options
- A comparative study of heat-treatment effects on high-strength ductile cast irons weldmentsPublication . Silva, Francisco José Gomes da; Sousa, V. F. C.; Pereira, A. B.; Fecheira, J. S.Ductile cast irons have known significant developments, closely following the evolution in mechanical strength recorded in other metal alloys. In fact, the chemical composition and treatments that ductile cast irons can currently be subjected to, give them mechanical strength far superior to the ductile cast irons that existed three decades ago, with rupture stresses in the order of 500 MPa and even higher. These properties combined with the fact that it is easy to manufacture parts with an almost final shape, makes these alloys highly sought after in some types of industry, such as the automotive industry. Due to the high content of carbon and other alloy elements with identical effects, welding is not a process that is seen as viable for the manufacture of parts in this type of alloys. However, the same is no longer the case in terms of repair, where welding can play a key role. Through a comparative study, this work intends to show that there is no single way to improve the mechanical properties in the welding of this type of alloys, and that each alloy should be properly studied in order to obtain the best results. In this case, the heat treatments applied to ductile cast iron with an ultimate tensile strength of 450 MPa and 700 MPa from the same manufacturer are compared, making it clear that to achieve the best results in terms of mechanical resistance, it is necessary to follow different routes, that is, choose to preheating or post-heating treatments, depending on the microstructure of the alloy used. Thus, the results obtained intend to show the mechanisms in which treatment is actually acting on the alloy, promoting greater efficiency of the joint and having been achieved interesting results at this level.
- Mechanical strength of thermoplastics and composite thermoplastics welded by laser – a reviewPublication . Pereira, A. B.; Fernandes, F. A. O.; Silva, Francisco José Gomes daThermoplastic welding is currently well implemented in the market, with several competitive and suitable processes, ranging from simple hot plate to ultrasonic welding. By its side, laser welding of plastics is still in a relatively early stage of research. This process is one of the most recent in the welding of thermoplastics and of great interest in the market. The welding technique is based on heating the thermoplastics by transmitting heat in the form of radiation. This is due to the ability of certain plastics to absorb the beam. Usually, one of the parts to be welded must be transparent and the other opaque to radiation. These two parts are kept under pressure as the laser beams are transmitted through the transparent part. The laser beam is concentrated in the joint area of the opaque part, heating and melting it. There are relatively few scientific studies on the joining of thermoplastics by laser and, in the case of thermoplastic matrix composites, there are even fewer. The main conclusion is that the mechanical strength of a laser welded joint is in the range of 30-50 MPa, a value that is frankly weak when compared to the value that the base material can handle and which is usually more than double for thermoplastics and 10 times for composites. Although the fusion process is contactless, one of the great limitations of laser welding of plastics is the need to exert pressure on the joint, which conditions and complicates the execution of a weld. However, despite everything, it is certain that laser welding presents mechanical strength values superior to those of a bonded connection and the processing time is much shorter, therefore, it is clear the interest on the process.
- Mode III interlaminar fracture of carbon/epoxy laminates using the edge crack torsion (ECT) testPublication . Morais, A. B. de; Pereira, A. B.; Moura, M. F. S. F. de; Magalhães, A. G.The mode III interlaminar fracture of carbon/epoxy laminates was evaluated with the edge crack torsion (ECT) test. Three-dimensional finite element analyses were performed in order to select two specimen geometries and an experimental data reduction scheme. Test results showed considerable non-linearity before the maximum load point and a significant R-curve effect. These features prevented an accurate definition of the initiation point. Nevertheless, analyses of non-linearity zones showed two likely initiation points corresponding to GIIIc values between 850 and 1100 J/m2 for both specimen geometries. Although any of these values is realistic, the range is too broad, thus showing the limitations of the ECT test and the need for further research.
- Quality assessment in the manufacture of a pressure piping by weldingPublication . Pereira, A. B.; Cardoso, J. P.; Silva, F. J. G.This chapter presents the necessary requirements for the CE marking of a pressure piping assembled in welded construction. The Quality Management of a welded construction involves well-regulated procedures which, however, are so vast that they acquire great complexity. In fact, there are hundreds of rules to apply to each specific case. In the European Union, the CE marking shows the presumption that the products comply with all the provisions of the applicable directives. This marking is a way to improve the safety of consumers, as well as the guarantee of having a competitive and regulated market, therefore good for the economy itself. Pressure equipment is, as a rule, considered dangerous, and therefore subject to strict and careful regulation. The CE marking is not established as a technical barrier, which prevents countries from exporting their products to the European market. It is just one way of harmonizing and unifying procedures, standards and legislation that has the purpose of completing the European internal market. This paper presents an analysis of how to obtain CE marking of an execution and assembly of steel piping in a formaldehyde plant and which normative ramifications apply.
- Quality assurance of welded construction of industrial boilersPublication . Pereira, A. B.; Martinho, J. C. F.; Silva, F. J. G.Quality assurance is an essential and indispensable requirement in metalworking. The obligation of manufacturers to comply with this requirement depends on the framework and scope applicable to the product. Thus, the manufacturer must not only know and respect the current legislation and regulations, but also the extensive standardization applicable to the products. Specially, manufacturers whose product is based on welded construction and subject to CE marking, have the obligation to know and implement all the necessary provisions for the conformity of the product from its conception to the availability of the product on the market. In this case, the objective of this work is to describe, specify and solve the various steps that allow a manufacturer of steam boilers to guarantee the quality in the welded construction of their product, with all that this implies. Nowadays the manufacturer's problem is not the quantity and capacity of the physical resources of manufacture, but rather the mastery of the technique and actuality of specific knowledge required to ensure the product compliance. A methodology to approach construction is proposed, assuming the manufacturer role, from the framing of the product to inspection and final testing. It is intended to detail and technically fully document each step, in accordance with the legislation and building codes applicable to the boiler under study.
- Recent developments on friction stir welding of aluminium alloys: a comprehensive reviewPublication . Silva, Francisco José Gomes da; Pereira, A. B.; Fecheira, J. S.; Sousa, V. F. C.Friction stir welding is a relatively new joining technology, that has been succefuly applied in the connection of large and complex structures, with considerable progress being made throughout time. The development of this new solid-state welding technique has opened up new possibilities for joining similar and dissimilar materials, allowing the obtention of extremely interesting mechanical properties. This welding technique becomes even more interesting when applied to materials that are traditionally considered difficult to weld by conventional fusion methods. As it is well known, despite the fact that aluminum alloys have a low melting point, these are difficult to weld due, mainly, to their high thermal conductivity, requiring relatively high amounts of energy, wich can interfere with the low melting temperature of the alloys. Thus, numerous studies have been carried out around the Friction Stir Welding (FSW) process in various different alloys, however, given the intensive use of aluminum alloys in the most diverse sectors, these have deserved special attention by the researchers. In this chapter, the welding of different aluminum alloys with different process parameters and their influence on mechanical property of the joints are analyzed. This review intends to describe, in a structured way, the most recent developments around FSW of aluminium alloys, with special attention given to the microstructure and mechanical properties of the joints obtained by this process, as well as the parameters able to achieve the best joint properties.