High Strength Steels Fracture Toughness Variation by the Media

The stress corrosion cracking process is at this moment an unknown mechanism of deterioration. It is a process that implies the joint action of the media, the presence of corrosion or a surface defect and of stress in the metal. Prestressing tendons can suffer SCC jointly with hydrogen embrittlement which dramatically changes not only the type of fracture (from ductile to brittle) but also the kinetics of the process leading to unexpected collapses. The metal should be resistant to this type of process which can be characterized by its toughness and therefore by its damage tolerance. This research shows that the Fracture Toughness change when the steel corrodes, questioning the idea that is an intrinsic characteristic of the material. The reduction in the fracture toughness of steel wires when they are in contact to aggressive media involve that the material fractures with a lower crack depth for the same stress level. That means that the material becomes less damage tolerant, which implies that it is necessary to detect defects of smaller size, as for example, small notch, pits or superficial cracks. In the paper some results of the percentage of decrease of the toughness of prestressing wires suffering corrosion are presented

Stress corrosion cracking and fracture toughness variation of high strength steels.

The stress corrosion cracking process is at this moment an unknown mechanism of deterioration. It is a process that implies the joint action of the media, the presence of corrosion or a surface defect and of stress in the metal. Prestressing tendons can suffer SCC jointly with hydrogen embrittlement which dramatically changes not only the type of fracture (from ductile to brittle) but also the kinetics of the process leading to unexpected collapses. The metal should be resistant to this type of process which can be characterized by its toughness and therefore by its damage tolerance. This research shows that the Fracture Toughness change when the steel corrodes, questioning the idea that is an intrinsic characteristic of the material. The reduction in the fracture toughness of steel wires when they are in contact to aggressive media involve that the material fractures with a lower crack depth for the same stress level. That means that the material becomes less damage tolerant, which implies that it is necessary to detect defects of smaller size, as for example, small notch, pits or superficial cracks. In the paper some results of the percentage of decrease of the toughness of prestressing wires suffering corrosion are presented

Hydrothermal monitoring using embedded sensors of the actual roof system of the prado museum

El Prado Museum in Madrid has been recently submitted to a refurbishment of its roof which from been made with the traditional tiles has been changed to the use of modern waterproofing layers covered with a metallic lead finishing. Due to an unexpected damp patch that produced leaking in the hall in which Las Meninas by Velázquez was exhibited, the authors were commissioned by the Ministry of Education and Culture to study the suitability of the roof and its waterproofing properties. The study led to suggestions of modifications in the design of the roof layers, which are out of the scope of present paper. In present paper are given the behaviour of the sensors embedded in two specific areas of the roof. The sensors installed were of: temperature, relative humidity, measurement of local strain and detection of liquid water. The liquid water sensors reveal that some water is withheld in the layer just below the thermal insulation material, although it is standing. The results of over four years of readings show that the temperature attenuates over distance away from the outermost layer, where the readings are very high in summer, due to it consists of lead. During the colder seasons, in turn, the temperature in the inner layers of the roof is higher than in the outer layers. The strain recorded follows the logical evolution of temperature with no abnormal behaviour being detected. Some of relative humidity sensors had measuring problems due to water condensing on them. In summary however, if the behaviour in this area is extrapolated to the rest of the roof, it can be considered to perform correctly as intended. No more leaking events have been detected from the design modifications were incorporated to the existing roof

Molecular Dynamics simulations of Hydrogen Embrittlement: preliminary results

Hydrogen embrittlement is believed to be one of the main reasons for cracking of structures under stress. High strength steels in these structures often include a ferritic core made of alpha-iron (body centered cubic lattice). Previous work [1] was concerned with the interaction of atomic hydrogen with iron using first principles calculations. We studied the effect of interstitial hydrogen in the iron lattice and the stress induced by the interstitial hydrogen in the host lattice. In this paper we study the dynamical behaviour of hydrogen inside the iron lattice. Using ab-initio Molecular Dynamics we obtain hydrogen diffusion paths and by taking statistical averages we extract diffusion coefficients from Einstein’s equation. Depending on temperature, the diffusion path involve going through tetrahedral or octahedral sites. Simulations where a number of hydrogens occasionally coincide in one unit cell have been performed to elucidate the effect of interactions between hydrogen

Procedimiento y dispositivo para la detencción de corrosión en acero enterrado protegido catódicamente, especialmente en las armaduras del hormigón o determinar si está pasivo.

Fecha de solicitud: 14.06.2002.- Titulares: Consejo Superior de Investigaciones Científicas (CSIC).- Geotecnia y cimientos S.A. (GEOCISA)[EN]The invention relates to a method for detecting corrosion in buried steel which, after containment of a carrier direct current, consists in: modulating an alternating current; determining the phase difference between the intensity of the alternating current and the alternating potential applied in order to ascertain whether or not the cathodic protection is effective, on the condition that the frequency interval of the alternating current is between 0.01 and 100 Hz. The measurement method consists in: (i) generating an alternating current which is applied between the buried steel and a counterelectrode located on the surface of the ground and (ii) using a standard electronic system, measuring the value of the applied voltage u and current i. Said values are subsequently processed electronically using a suitable device in order to determine phase angle n, the value of which indicates the effectiveness of the cathodic protection. [ES]La presente invención se basa en que, tras el confinamiento de una corriente continua portadora, se modula una corriente alterna el desfase entre la intensidad de corriente alterna y el potencial alterno aplicado permite conocer si la protección catódica es eficaz, siempre que el intervalo de frecuencias de la corriente alterna esté comprendido entre 0.01 y 100 Hz. El procedimiento de medida consiste en generar una corriente alterna que se aplica entre el acero enterrado y un contraelectrodo situado en la superficie del terreno mediante un sistema electrónico convencional se mide el valor de la tensión u y la corriente i aplicada, las cuales, computarizándolasen un dispositivo adecuado, permiten conocer el ángulo de fase n, cuyo valor indica la eficacia de la protección catódica.Peer reviewe

Desarrollo sostenible : una meta para el entorno educativo : becas de investigación didáctica patrocinadas por El Corte Inglés

Concurso de becas: Investiga a través del entorno y exponlo. Contiene un folleto anexo con las bases de la XIX edición del concurso, para el curso 2005-06Se recogen las memorias de los proyectos de innovación becados en la XVI y XVII edición del concurso 'Investiga a través del entorno y expongo' 2002-2004, patrocinado por El Corte Inglés, cuyo tema principal es el desarrollo sostenible. En cada uno de los proyectos se ofrece un resumen de la experiencia y de la exposición organizada. Se presentan también reflexiones y opiniones de expertos sobre el desarrollo sostenible en su vertiente científica y didáctica.MadridBiblioteca de Educación del Ministerio de Educación, Cultura y Deporte; Calle San Agustín 5 -3 Planta; 28014 Madrid; Tel. +34917748000; [email protected]