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El fuego es un factor ecológico cuya presencia desde tiempos inmemoriales ha moldeado la vegetación. Para algunos ecosistemas este factor es tan importante como pueden serlo el sol o la lluvia. Por otra parte, los homínidos conquistaron el fuego y después fueron capaces de producirlo, convirtiéndose para ellos en una herramienta inseparable, tan importante que les permitió dar un salto en su desarrollo y conquista del planeta como nunca ha podido hacerlo otra especie. Durante mucho tiempo la vegetación en la Tierra se desarrolló bajo diferentes regímenes naturales de fuego, ante los cuales los ecosistemas eran resilientes. Poco a poco estos regímenes se alteraron debido, entre otras cosas, a políticas bien diseñadas de protección contra incendios forestales, pero que lamentablemente no consideraron la importancia del fuego como factor ecológico, el aumento de la población, la pobreza y las áreas plantadas con especies forestales inflamables, así como el uso del fuego en actividades agrícolas y, finalmente, el cambio climático. Como resultado, hoy día muchas regiones del mundo viven situaciones de emergencia debido al aumento del número de incendios y de las áreas quemadas, todo lo cual trae destrucción de la vegetación, de viviendas y de todo tipo de infraestructuras, incluyendo a veces la pérdida de vidas humanas. Incendios Forestales Investigaciones sobre el comportamiento histórico de los incendios forestales es un texto que busca hacer un modesto aporte desde la academia al tema del manejo del fuego. Constituye una herramienta tanto para decisores como para investigadores, docentes y estudiantes que sientan interés por el tema tratado. Poder cumplir con las expectativas de todos, sería nuestra máxima aspiración.

La presente investigación se ejecutó dentro del marco del proyecto "Conservación y manejo sostenible del bosque seco tropical en el marco de la implementación de medidas de adaptación al cambio climático basado en ecosistemas”, fomentado por el Fondo Ítalo-Ecuatoriano para el Desarrollo Sostenible (FIDES), en conjunto con la carrera de Ingeniería Forestal de la UNESUM; con el enfoque de enriquecer o recuperar los bosques, el objetivo de este trabajo fue evaluar la diversidad arbórea en las áreas degradadas de la comunidad Quimis; para el registro de datos se identificaron zonas boscosas degradadas en las cuales fueron establecidas 23 parcelas donde se identificó y recolectó muestras botánicas de cada una de las especies presentes dentro de las parcelas, con la información obtenida se identificó la composición arbórea y realizó un análisis de diversidad utilizando el índice de Shannon-Weaver, encontrándose 769 individuos, 14 familias arbóreas, 21 géneros y 21 especies; según el Índice de Valor de Importancia Ecológica las especies forestales de menor potencial prioritario para la restauración ecológica fueron: Capparicordis crotonoides, Machaerium millei y Gallesia integrifolia y las 18 especies restantes son consideradas de prioridad media.

Resumen Los análisis del comportamiento histórico de los incendios forestales suministran informaciones imprescindibles para la elaboración de programas eficaces de manejo del fuego en los territorios. Estos análisis permiten definir dónde, cuándo y por qué se producen los incendios. El objetivo de este trabajo fue analizar el comportamiento histórico de los incendios forestales en el Cantón Rocafuerte, Manabí, Ecuador, en el periodo 2016 al 2019. Los datos fueron suministrados por el Cuerpo de Bomberos de Rocafuerte. El análisis se realizó considerando las ocurrencias de incendios en un contexto espacio-temporal (años, meses, días de la semana, horas del día y localidades). El análisis estadístico se realizó con el programa SPSS Statistics for Windows (Version 22.0). Se trabajó con un nivel de significancia del 0,05 (p=0,05). En el periodo analizado se reportaron 309 ocurrencias, correspondiendo al año 2018 el mayor porcentaje (30,42 %). La media mensual de ocurrencias fue de 25,75 superándose este valor en seis meses (diciembre, enero y junio a septiembre) correspondiendo a ellos el 61,48 % del total de incendios. No se encontró diferencia estadísticamente significativa para las ocurrencias según los días de la semana (p=0,650) según los resultados del Análisis de Varianza. Los incendios ocurrieron en 51 localidades del Cantón Rocafuerte concentrándose en seis de ellas el 60,52 % del total. El 52,43 % de los incendios se originó por negligencias. Abstract The analysis of forest fires historical behavior provides essential information for the development of effective fire management programs in the territories. These analyzes allow to define where, when and why fires occur. The objective of this work was to analyze the forest fires historical behavior in the Rocafuerte Canton, Manabí province, Ecuador, in 2016 to 2019 period. The dates were provide by the Fire Department of Rocafuerte. The analysis was made considering the occurrences of fires in a spatio-temporal context (years, months, days of the week, hours and localities). Statistical analysis was performed with SPSS Statistics for Windows (Version 22.0). We worked with a significance level of 0.05 (p=0.05). In the analyzed period, 309 occurrences were reported, corresponding to 2018 the highest percentage (30.42 %). The average monthly occurrence was 25.75, exceeding this value in six months (December, January and June to September) corresponding to them 61.48 % of total fires. No statistically significant difference was found for the occurrences to the days of the week (p=0.650) according to the ANOVA results. The fires occurred in 51 locations, with 60.52 % of the total concentrated in six of them. The 52.43 % of fires was originated from negligence.

The book provides research methodologies conducted in different contexts and from the perspective of several universities, so they are for teachers who teach the subject of fire management or forest fires in pre and postgraduate, tools to develop similar work in other regions. In turn, the results obtained in these investigations can help the discussion of those obtained in future work. Also the production specialists are nourished by new knowledge that will surely contribute to their professional performance.

International audience; In a hot strip mill, the contact established between the hot strip and the work rolls in the first times of running has to be oxide on oxide to allow the strip to be pulled in the roll bite. The oxide scale formed on the roll is submitted to thermo-mechanical stresses and grows up. From a critical thickness, the scale spalls and causes some superficial damage to the rolls and to the strip. For the roll manufacturers as well as for the steel makers, it is essential to understand the influence of the creation and the growth of such a scale on friction in order to control the antagonist superficial damage and consequently to reduce the running cost of the mill. The present work aims to study the interaction between the oxides formed on a work roll grade and the coefficient of friction established with a strip steel usually rolled by this roll grade. A high temperature tribometer was set up in a pin-on-disc configuration. A previous part of study showed that friction was dependent on the nature of antagonist materials and the thermal transfer. We observed the establishment of a running-in period in the case of a metal-on-oxide initial contact between the pin and the disc which corresponds to the creation of an oxide layer on the pin. The mechanisms that allowed the formation of this scale were determined. SEM observations in conjunction with EDS analysis, both inside and outside the contact area on both antagonists, led to the development of a phenomenological model explaining the creation and the movement of oxide debris in the contact.

Issu de : WOM 09 - 17th International Conference on Wear of Materials 19-23 April 2009 • Las Vegas, USA; International audience; Given the specific micro‐structure of some steel grades, under tribological conditions the sub‐surface material or sub‐layers of sliding bodies are prone to cumulative cyclic plastic deformation, leading to the formation and emission of wear debris. In the present paper, a new wear model based on a cyclic ratchetting‐type plastic deformation of subsurface material is proposed. It is considered that the debris is formed and the wear‐loss occurs when the accumulated plastic deformation at sub‐surface exceeds ``a critical strain'' or ``rupture limit''. The model takes into account the number of cycles or test duration, a characteristic thickness of the sub‐layer dependent on tribological conditions and material properties, the shear rupture ductility and an average plastic strain increment. The average plastic strain increment is estimated by numerical simulation of pin‐on‐disc friction. A very close correlation is found between the predicted and experimental wear heights versus time and/or versus the number of cycles. The wear investigations were carried out on a high‐temperature pin‐on‐disc tribometer under dry friction conditions. Experiments were performed under constant load, speed and disc temperature for different durations. The steel grade involved was a tempered martensitic tool steel X38CrMoV5 (AISI H11). Wear mechanisms were investigated by Scanning Electron Microscopy (SEM) observations in surface and cross‐section.

16th International Conference on Wear of Materials 15-17 April 2007 • Montreal, Canada; International audience; The wear rate of sliding materials seems impossible to predict. It is clearly a function of substrate material, but we are learning that many surface events are also important. In particular, studies on the last 20 years have shown that substances develop between two sliding bodies have a strong influence on both friction and wear. These substances had become known as "third bodies". Whereas third bodies have been proven to be important, they have not been completely characterized. The third bodies have been studied, but it appears that the geometries of the sliding pairs are also important. This paper describes some experiments in which the composition of third-body materials are controlled by temperatures and in which the durability of third-body films are influenced by the geometry of contact between sliding bodies.

International audience

International audience; A significant part of the energy in forging is used to break the interfacial junctions due to friction between the tool and the workpiece. The life of hot‐forging tools is usually limited by complex interactive mechanisms under cyclic loading such as abrasive, adhesive and scaling wear, thermal and mechanical fatigue, and plastic deformation. This contribution deals with the wear mechanisms of the tempered martensitic X38CrMoV5 steel (AISI HI 1) under high‐temperature and dry‐sliding wear. The investigations are carried out with high‐temperature pin‐on‐disc tests. The pin is cut from bars of X38CrMoV5 steel treated at 42 and 47 HRC. The disc is made of common steel (AISI 1018, XC18). Temperature of the disc ranges from 20 to 950 degreesC. Before the test starts, the disc is first pre‐heated for 1 h. The experiments are performed under constant load and velocity. The friction coefficient decreases quasi‐linearly with the rising disc temperature up to 800 degreesC. Over this temperature, it decreases drastically for the 42 HRC steel but remains linear For the 47 HRC steel. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) investigations have revealed that wear is essentially due to abrasion, plastic deformation and fatigue. Set of cracks due to contact rolling fatigue is observed on the pin and the disc. Those cracks are located on the transferred scale on the pin and on the oxide scale of the disc wear track. The cross‐section observations of the pin have revealed a plastically deformed zone beneath the surface. In this sub‐surface layer, the tempered martensitic microstructure seems to be more aligned due to friction and the plastic deformation.

This article concerns the evaluation of the friction coefficient in the particular case of mixed lubrication between parallel surfaces. We shall compare the experimental results and those obtained by means of the model we have developed. To this end, we evaluate the friction coefficient at two distinct scales. One concerns the full contact analysed in terms of juxtaposed asperities working in either direct contact (elastic or elasto-plastic or fully plastic deformation) or in lubricated contact (hydrodynamic or elastohydrodynamic regimes). The second involves evaluating at the asperity scale and concerns both lubricated regimes. Experiment and theory closely agrees in the cases of full contact and hydrodynamic asperity contact. As concerns the elastohydrodynamic regime further adjustments in the model are required.

13th International Conference on Wear of Materials, VANCOUVER, CANADA, APR 22-26, 2001; International audience; in hot forming processes, the interface tool/product is important for the quality of the finished product. In hot rolling, the scale formed on the roll material plays an essential role. As soon as the contact oxide-oxide is established between the roll and the slab, friction allows the process to start. However, the oxide scale will continue to grow under the cyclic action of hot contacts and water cooling, and will be subjected to thermo-mechanical stresses. Beyond a certain critical thickness, the oxidized surface layer of the cylinders has not sufficient mechanical strength to withstand the shear stresses. The wear and friction behavior of the oxides appearing on the surface of the hot working rolls is not well known. The influence of these oxides on the friction and, consequently, the quality of the products of finishing mills, seems very significant. So, in this study, we investigate the evolution of the friction coefficient and the wear, according to the growth, the nature and the thickness of the formed scale. We use a high temperature pin on disc tribometer. The pin consists of material ``rolls'' while the disc consists of the slab. The pin is instrumented with thermocouples in order to couple the friction coefficient measurements with the thermal gradient in the pin and the surface temperature and the formed oxides, Then, the characterization of the surfaces is done by scanning electronic microscopy (SEM) and EDS analyses. We use the method of sin(2) Psi to evaluate residual stresses of oxide and correlate these data with shear stress behavior.

National audience

Resume On a etudie a l'aide du frictiographe haute temperature sous vide de l'I.S.M.C.M. l'effet de la temperature ambiante sur le frottement du titane et de l'alliage TA6V. Si on examine la courbe montrant la variation de la force de frottement en fonction de la temperature on observe dans les conditions d'essais l'existence de deux phases. La premiere correspond a un frottement regulier, une usure peu importante et des degâts superficiels faibles. La seconde phase apparait a une temperature critique d'environ 300°C. Elle correspond a un frottement tres eleve avec des endommagements importants sur les surfaces. Au-dela de cette temperature, on observe des liaisons interfaciales plus resistantes que le metal de base entrainant un cisaillement de ce dernier en-dessous de la surface. On demontre dans le domaine de temperature etudie que ces liaisons sont dues a l'interpenetration des materiaux causee par une action combinee de la temperature et des contraintes qui Simultanement affaiblissent les souscouches et favorisent l'adhesion. En modifiant la structure metallurgique des couches superficielles du TA6V sur une certaine epaisseur, par un traitement de nitruration on retarde notablement l'apparition de ce seuil critique. On peut encore ameliorer les qualites frottantes des alliages traites en choisissant un contre materiau tel qu'une stellite a base de cobalt plus compatible avec le titane et conservant de meilleures caracteristiques mecaniques a chaud.

Goudineau Christian, Gras Rene. La ceramique grise gallo-romaine. Note complementaire. In: Revue archeologique de Narbonnaise, tome 11, 1978. pp. 195-212.

National audience

Extrait de : Matériaux, usures et corrosion - 38èmes Journées du cercle d'études des métaux, Liège, BELGIQUE, 26-27 mai 1999; International audience