Papers by Author: Angel Varela

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Authors: Ana García, Laura Ferreiro, Angel Varela, José Luís Mier, Carolina Camba, Fernando Barbadillo
Abstract: Wear is one of the most worrying problems in industry; it affects many production sectors. Therefore, the wear resistance of materials must be assessed in order to predict their response and anticipate possible failures. Maintenance could then be scheduled accordingly. Due to the large number of situations where wear is important, one of the main complications in tribology is that it is difficult to replicate in a laboratory the precise conditions of service. Thus, there is a need to choose between different kinds of tests to simulate actual conditions. However, this aim is difficult to achieve, as variables and conditions of service are numerous. In this situation, it is neither practical nor possible to have as many test devices in the laboratory as real possibilities. It is necessary to find a test that can be extrapolated to many possible situations. An important question is if the results obtained with different configurations simulated in the laboratory are good equivalents or, on the contrary, the choice of method has an influence and to what extent the latter case is true. In addition, it should be noted that wear test standards mention how difficult it is to reproduce results and how they are influenced by operating conditions In this paper, three wear tests methods are studied- the pin-on-disk, dry sand/rubber wheel test and wet sand/rubber wheel- in order to find a relationship between the results obtained by them. Furthermore, different techniques are analysed to establish, if possible, which ones are more likely to achieve more reliable results.
Authors: Angel Varela, Ana García, José Luís Mier, Ramón Artiaga, Fernando Barbadillo, L. García
Authors: Ramón Artiaga, Angel Varela, José Luís Mier, Ana García, Rosa Losada, Salvador Naya
Authors: Rosa Losada, José Luís Mier, Fernando Barbadillo, Ramón Artiaga, Angel Varela, Salvador Naya
Abstract: A diglycidyl-ether of bisphenol-A (DGEBA)/Triethylenetetramine (TETA) system was studied by non-isothermal differential scanning calorimetry (DSC) to establish its kinetics of cure. The DGEBA resin was Araldite GZ 601 X75 used in the marine coatings formulations. Previously, the optimum resin/hardener ratio was determined by the reaction heat measuring (.Hc) calculated from the curing exothermic peak. Tests at different heating rates (10, 15, 20, 25 and 30°C/min) under inert atmosphere were carried out in order to study the reaction kinetics. The activation energy of the cure (Ea) was obtained from these tests data by Borchardt-Daniels, autocatalytic, Duswalt and isoconversional Ozawa methods. Once the activation energy was determined, the master curves method was applied to find the kinetic model which best describes the measured DSC data. The Sestak-Berggren model SB (m,n) was found to be the most adequate for the system studied.
Authors: Ana García, Angel Varela, J. Montero, José Luís Mier, S. Zaragoza, Fernando Barbadillo
Abstract: This work studies the behaviour of welding joints under abrasive wear in A355 Gr. P11 steel pipes carrying liquids at high temperatures. Various welding processes were tested on different joints in an effort to choose the one that gave the best wear response. For this purpose, a pin-on-disk tribometer was used at 200°C to simulate the service conditions of the pipes. The tests were carried out by pressing a hard chromium-plated steel pin, with a diameter of 4 mm and hardness of about 775 HV, on steel specimens in order to measure their mass loss and friction coefficient in the three welding zones: base metal (BM), heat affected zone (HAZ) and weld bead (WB). The tests conditions were 10 N of load, 200 rpm of rotation velocity and a radius of 3 mm. In addition, metallographic studies and hardness measurements of the three welding zones were done to complete this work.
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