Departamento de Ingeniería Mecánica y Minera
URI permanente para esta comunidadhttps://hdl.handle.net/10953/41
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Ítem Effect of crack flank holes on fatigue crack growth(Elsevier, 2023-01-07) Neto, Diogo Mariano; Cavaleiro, Nuno; Sérgio, Edmundo; Jesus, Joel de; Camacho-Reyes, Alonso; Antunes, Fernando VenturaThe effect of drilling two symmetric holes along the crack flanks on the fatigue crack growth (FCG) rate was evaluated numerically. The FCG increases (decreases) when the crack tip is behind (ahead) the holes. This behaviour is enlarged both by increasing the diameter of the holes and by reducing the distance between them. This is consequence of the geometrical effect, which modifies the plastic zone size. Experimental work validated the numerical model, indicating that that cumulative plastic strain at the crack tip is an adequate crack driving force and that cyclic plastic deformation is the main damage mechanism of FCG.Ítem Estudio numérico de la fisuración de traviesas monobloque polivalentes de hormigón pretensado instaladas en la vía(2025-03) Donaire-Ávila, Jesús; Fernández-Aceituno, Javier; Suárez-Guerra, FernandoLas traviesas monobloque polivalentes de hormigón pretensado permiten adoptar tanto anchos de vía estándar (1435 mm) como ibérico (1668 mm). Se ha observado en ellas la presencia de fisuración longitudinal, tanto en las acopiadas como en las instaladas en la vía. En este estudio se analiza la evolución en la apertura de fisura durante las fases de fabricación, acopio e instalación en la vía (incluyendo la neutralización de tensiones y la fijación de carriles), considerando las acciones térmicas y mecánicas del proceso, excluyendo las producidas por el ferrocarril. Se utiliza para ello un modelo numérico no-lineal validado experimentalmente. Se evalúa el grado de fisuración de traviesas fabricadas con hormigón de árido calizo y vainas poliméricas de alto módulo de deformación para la fijación directa de carriles mediante el sistema SKL. Los resultados muestran que el grado de expansividad térmica y de rigidez de las vainas junto con el nivel de la temperatura ambiente son aspectos que influyen de forma determinante en el nivel de fisuración y en la capacidad para la fijación de las traviesas, sobre todo en aquellas fabricadas en época fría e instaladas en ambiente cálido.Ítem Hydraulic control on the development of megaflood runup deposits(Elsevier, 2020-04-07) Carling, Paul Anthony; Bohórquez, Patricio; Fan, XuanmeiRunup deposits are veneers of alluvium that drape floodway valley side walls above the height of giant bars deposited during megafloods. Given sufficient sediment supply, the highest giant bars, deposited in re-entrants along the flood margins, tend to grow to close to the maximum time-averaged water level of the flood. However, considerable fluctuations in the water level, caused by sediment-charged floodwaters surging over shorter time-scales, are responsible for the higher runup deposits. Here, the theoretical calculations of the expected maximum runup heights are compared with surveyed heights of six runup deposits in the Chuja Valley, Altai, Siberia. The limitations and strengths of the theoretical approach are identified and modified parameters proposed that can be used to provide partial explanation for the differences between theory and observation. Conceptually, surging can be viewed as caused by four interrelated elements: (1) propagation of undular weir flow; (2) macroturbulence; (3) flow separation; and (4) standing, reflection and interference waves. The heights of the observed runup deposits primarily are related to the depth of the flood water above the bar tops and, to a lesser extent, the Froude number, but tend to lie below the maximum surge heights of the modelled flow. Changes in the effective geometry of the flow re-entrant, mediating flow patterns, as water depth increases is likely the cause of mismatch between theory and observation. Runup deposits may also lie at lower elevations than predicted because of sediment supply considerations and the return flow of surges ‘combing’ down deposits. Nonetheless, the difference between observed and predicted runup heights is often only a few tens of metres such that, for deep floods, runup deposits potentially are useful palaeostage indicators. The analysis also indicates that upper-stage plane beds do not dominate bar tops, rather bar top deposition was primarily to lower-stage plane beds, from dense suspensions.Ítem Limitations of small-scale yielding for fatigue crack growth(Elsevier, 2021-05-28) da-Silva-Veloso-Marques, Bruno Miguel; Borges, Micael Frias; Antunes, Fernando Ventura; Vasco, José Manuel; Diaz-Garrido, Francisco Alberto; James, NeilThe work described here has led to a simple criterion that defines the boundary of the small-scale yielding, SSY, regime to avoid invalid use of the LEFM parameter, ΔK, as the characterising parameter for fatigue crack growth rate. The approach proposed is based on the analysis of crack tip opening displacement, CTOD, and its separation into elastic and plastic components. SSY conditions are shown to dominate when the elastic component of CTOD is >75% of the total CTOD measured at a distance of 8 μm (the finite element mesh size) behind the crack tip, i.e., Δδe/Δδt > 75%. Large-scale yielding, LSY, conditions become dominant for relatively large values of plastic CTOD, Δδe/Δδt < 60%. An increase in crack length (and therefore of ΔK), a decrease in yield stress of the material and the existence of plane stress conditions all promote LSY. The results obtained from various loading and geometric conditions simulated in this work demonstrate that caution should be used in assuming that the use of ΔK is valid even for high strength alloys like Ti6Al4V. In this material, the boundary of the elastic regime was crossed and SSY conditions lost, for the longest crack lengths studied and in the case of overloads.Ítem Measurement of railroad track irregularities using an automated recording vehicle(ELSEVIER, 2021) Urda, Pedro; Fernández-Aceituno, Javier; Muñoz-Moreno, Sergio; Escalona, José LuisThis paper presents the design, construction and experimental validation of a scaled railway vehicle for the automated and quick survey of the geometry of an experimental scaled track. The method, that can be extended to full scale tracks, validates the measurements of the automated recording vehicle (ARV) by comparison with respect to a precise but slow manual measuring method (MMM). The two-axle vehicle, which is powered by a brushless DC motor, has its leading axle instrumented with a LVDT, an inclinometer, a reflector and a precisIon encoder. These sensors, together with the help of a total station, allow the measurement of the scaled track geometry and its irregularities following an optimization procedure that first determines the ideal track centreline. The ARV has been tested on a scaled track and its measurements are validated with the MMM results showing a good agreement between both approaches.Ítem On strain localization under bending(2014-07) Jirásek, Milan; Suárez Guerra, FernandoThe aim of the present contribution is to assess the localization properties of nonlocal damage models under bending. To permit a partially analytical treatment and to display the fundamental properties of various formulations, the idealized case of uniform bending is considered. This means that the beam has a constant cross section and is subjected to a uniformly distributed bending moment and zero normal force. The beam is assumed to be very long, and boundary effects that might be introduced by the supports at the end sections are eliminated by imposing periodic boundary conditions on the fluctuating part of the response, which is superimposed on the solution that corresponds to uniform curvature. The average curvature serves as a loading parameter that is monotonically increased.Ítem Technological advances to rescue temporary and ephemeral wetlands: reducing their vulnerability, making them visible(MDPI, 2023-07-15) Jiménez-Melero, Raquel; Bohórquez, Patricio; González-Planet, Inmaculada; Pérez-Latorre, Francisco; Parra-Anguita, GemaMediterranean temporary ponds are a priority habitat according to the Natura 2000 network of the European Union, and complete inventories of these ecosystems are therefore needed. Their small size, short hydroperiod, or severe disturbance make these ponds undetectable by most remote sensing systems. Here we show, for the first time, that the distributed hydrologic model IBER+ detects ephemeral and even extinct wetlands by fully exploiting the available digital elevation model and resolving many microtopographic features at drainage basin scales of about 1000 km2. This paper aims to implement a methodology for siting flood-prone areas that can potentially host a temporary wetland, validating the results with historical orthophotos and existing wetlands inventories. Our model succeeds in dryland endorheic catchments of the Upper Guadalquivir Basin: it has detected 89% of the previously catalogued wetlands and found four new unknown wetlands. In addition, we have found that 24% of the detected wetlands have disappeared because of global change. Subsequently, environmental managers could use the proposed methodology to locate wetlands quickly and cheaply. Finding wetlands would help monitor their conservation and restore them if needed.