Residual stresses in thermite welded rails: significance of additional forging

The aluminothermic welding (ATW) process is the most commonly used welding process for welding rails (track) in the field. The large amount of weld metal added in the ATW process may result in a wide uneven surface zone on the rail head, which may, in rare cases, lead to irregularities in wear and plastic deformation due to high dynamic wheel-rail forces as wheels pass. The present paper studies the introduction of additional forging to the ATW process, intended to reduce the width of the zone affected by the heat input, while not creating a more detrimental residual stress field. Simulations using a novel thermo-mechanical FE model of the ATW process show that addition of a forging pressure leads to a somewhat smaller width of the zone affected by heat. This is also found in a metallurgical examination, showing that this zone (weld metal and heat-affected zone) is fully pearlitic. Only marginal differences are found in the residual stress field when additional forging is applied. In both cases, large tensile residual stresses are found in the rail web at the weld. Additional forging may increase the risk of hot cracking due to an increase in plastic strains within the welded area

Stratified surface layers on rails

This study examines the properties of stratified surface layers on rails in service and presents a hypothesis explaining their origin. The stratified layer consists of a white etching top layer and a brown sublayer. The metallurgical composition and properties of this sublayer are found to match with that of globular bainite. The occurrence of stratification in the surface layer is explained by the thermomechanical cycle for a material point on the rail surface under wheel-rail contact. Difference in the surface and subsurface cooling rates after reaching the austenitisation temperature may lead, depending on the chemical steel composition, to the generation of two different phases (martensite and bainite) and stratification. The exclusive occurrence of sandwich layers on rails that have been in service is attributed to the hardening of the top layer, leading to a reduced thermal conductivity, which gains relevance at an increasing depth. The granular morphology of the bainitic sublayer, exhibiting weak globular inclusions, facilitates the initiation and the propagation of transverse cracks, thus contributing to the development of RCF.Railway Engineerin

Friction modifiers effects on tribological behaviour of bainitic rail steels

Bainitic steels are gaining popularity for application in the railway switches and crossing, thanks to their better rolling contact fatigue (RCF) and wear resistance. The rail degradation caused by RCF and wear could be also reduced by the use of friction modifiers (FM) through their ability to reduce the lateral load during wheel passage. This paper presents the microstructure and the mechanical properties of newly designed bainitic steel grades; B1400 + and Cr–B potential candidates for switches and turnouts railroad industry. It investigates their friction and wear performances using the HOrizontal twin DIsk Machine. The tribological behavior is evaluated under dry and lubricated conditions in combination with three commercial friction modifiers. Results show a better wear resistance of Cr–B steel in case of abrasive mechanism that dominates the dry experiments. This work defines the efficiency of FM as a low and stable friction coefficient concomitant to a low wear rate. It appears that a good tribological performance is untimely linked to the chemical composition of the friction modifier. In case of lubricated contact, cross-sectioning of wear scare confirms the generation of an interfacial layers. These layers have an impact on the wear mechanism and debris detachment susceptibilities of bainitic steels.Accepted Author ManuscriptRailway Engineering(OLD) MSE-

Investigation of the percentage and the compacting pressure effect on the structural, optical and thermal properties of alumina-zeolite mixture

This paper presents a detailed investigation of the correlation between micro-structural, optical and thermal properties of a mixture constituted of NaA zeolite and Al2O3 alumina with different portions at various compacting pressures. A comprehensive study was made by using SEM, EDX, XRD, PL and PTD analysis. Through this full characterization, it was demonstrated that a mixture of grain size ranging from 50 nm to 85 nm can be used as a red emitter of mean wave length λ=650μm in optical devices. This mixture also proved to be used as a thermoinsultor or a thermocondensor material; with a thermal conductivity of about 0.22–1.33 W·m−1·K−1 and a thermal diffusivity of about 0.070–0.174 cm2·s−1. Keywords: NaA zeolite, Alumina, Photoluminescence, Thermal propertie

Residual stresses in thermite welded rails: significance of additional forging

The aluminothermic welding (ATW) process is the most commonly used welding process for welding rails (track) in the field. The large amount of weld metal added in the ATW process may result in a wide uneven surface zone on the rail head, which may, in rare cases, lead to irregularities in wear and plastic deformation due to high dynamic wheel-rail forces as wheels pass. The present paper studies the introduction of additional forging to the ATW process, intended to reduce the width of the zone affected by the heat input, while not creating a more detrimental residual stress field. Simulations using a novel thermo-mechanical FE model of the ATW process show that addition of a forging pressure leads to a somewhat smaller width of the zone affected by heat. This is also found in a metallurgical examination, showing that this zone (weld metal and heat-affected zone) is fully pearlitic. Only marginal differences are found in the residual stress field when additional forging is applied. In both cases, large tensile residual stresses are found in the rail web at the weld. Additional forging may increase the risk of hot cracking due to an increase in plastic strains within the welded area.Railway Engineerin

Comment on "Reinterpretation of the thickness-dependent conductivity of thin platinum films"

Vancea J, Reiss G, Hoffmann H. Comment on "Reinterpretation of the thickness-dependent conductivity of thin platinum films". Journal of Materials Science Letters. 1987;6(8):985-986

Associations entre les temps d’écran et les habitudes de sommeil chez des jeunes collégiens

Screen media usage has become increasingly commonplace in daily life with children initiating themselves to screen media at an early age. Given the high prevalence of screen viewing among children worldwide, its impact on children's health has become a cause for concern. Unfortunately, little information on the independent association between sleep habits and screen time in French children is currently available. The main aim of this study was to assess possible relationships between screen time and sleep habits (quality, duration, etc.) among young middle school students in France. A total of 448 (55 % girls) 11-to-12-year-olds from 5 schools were included. Body weight and height were measured according to standard procedures and BMI percentiles were determined based on international reference values. Sleep parameters were obtained by sleep diaries and visual estimations. A sleep diary was maintained for one week to record sleeping and waking times and related information. Information on lifestyle habits (sedentary behaviours, physical activity, and dietary intake) was obtained via standardised questionnaires. Participants were 11.5 (±0.4) years of age. From total sample, 25.5 % reported screen time ≥2hours/d during school days and 62.7 % during school-free days. High screen time was associated with significantly poorer sleep habits and these results remained valid after adjustment for several confounding factors (body mass index, sex, center and parental level of educational attainment) (P<0.05). This study highlights an association between longer screen time and shorter sleep duration in French middle school students aged 11 to 12 years. Preventive measures on use of and exposure to screens are called for. Further studies are necessary to confirm our findings.L’utilisation des écrans est aujourd’hui courante dans la vie quotidienne et de plus en plus précoce chez les enfants. Compte tenu de la forte prévalence de cette utilisation, l’impact sur la santé des enfants est source de questions. Des informations limitées sont disponibles sur l’association entre les habitudes de sommeil et le temps passé devant un écran chez les enfants français. L’objectif principal de cette étude était d’évaluer la relation entre le temps d’écran et les habitudes de sommeil des jeunes collégiens. Un total de 448 (55 % de filles) jeunes collégiens âgés de 11 à 12 ans, issus de 20 classes de cinq établissements, ont été inclus. Le poids corporel et la taille ont été mesurés selon les procédures standards et les centiles d’IMC ont été déterminés. Les paramètres du sommeil ont été obtenus par des agendas du sommeil et des estimations visuelles. Un journal du sommeil a été tenu pendant une semaine pour enregistrer les heures de sommeil et de réveil et les informations connexes. Des informations sur les habitudes de vie (comportements sédentaires, activité physique et apport alimentaire) ont été obtenues via des questionnaires standardisés. Les participants étaient âgés de 11,5 (± 0,4) ans et 25,5 % ont déclaré un temps d’écran ≥ 2 heures/jour pendant les jours d’école et 62,7 % pendant les jours sans école. Un temps d’écran élevé était associé à des habitudes de sommeil significativement moins bonnes même après ajustement sur plusieurs facteurs confondants (indice de masse corporelle, sexe, centre et niveau d’éducation parentale) (p < 0,05). Cette étude montre une association entre un temps d’écran plus long et une durée de sommeil plus courte chez les jeunes collégiens âgés de 11 à 12 ans. Des mesures préventives concernant l’utilisation des écrans sont nécessaires. D’autres études sont nécessaires pour confirmer nos résultats

Leishmaniasis in central and southern Tunisia: current geographical distribution of zymodemes

The authors report the identification of Leishmania strains isolated from the Centre and the South of Tunisia. 266 strains were isolated between 1998 and 2006 from human (n = 221 strains) and dogs (n = 45 strains) hosts. The isoenzymatic identification exhibits the presence of in total five zymodemes belonging to three Leishmania complexes: Leishmania infantum, L. major and L. killicki. All strains isolated from human and canine visceral leishmaniasis belonged to L. infantum. zymodeme MON-1 was the only one isolated from canine visceral leishmaniasis. However, it is predominant in human visceral leishmaniasis beside zymodeme MON-24 which was detected in two provinces of the Centre (Monastir and Kairouan) and zymodeme MON-80 isolated for the first time in Kairouan province. Three complexes are responsible for human cutaneous leishmaniasis: L. major MON-25 is the parasite the most frequently found in its classic foci in the Centre and the South of the country. L. infantum MON-24 was isolated for the first time in a small locality of Sfax (southern Tunisia) showing the appearance of a new focus of L. infantum. L. killicki was isolated in its original focus of Tataouine and in two new foci of the central part of the country (Sidi Bouzid and Kairouan)

Leishmaniasis in central and southern Tunisia: current geographical distribution of zymodemes

International audienceThe authors report the identification of Leishmania strains isolated from the Centre and the South of Tunisia. 266 strains were isolated between 1998 and 2006 from human (n=221 strains) and dogs (n=45 strains) hosts. The isoenzymatic identification exhibits the presence of in total five zymodemes belonging to three Leishmanio complexes: Leishmania infantum, L. major and L. killicki. All strains isolated from human and canine visceral leishmaniasis belonged to L. infantum. zymodeme MON-1 was the only one isolated from canine visceral leishmaniasis. However, it is predominant in human visceral leishmaniasis beside zymodeme MON-24 which was detected in two provinces of the Centre (Monastir and Kairouan) and zymodeme MON-80 isolated for the first time in Kairouan province. Three complexes are responsible for human cutaneous leishmaniasis: L. major MON-25 is the parasite the most frequently found in its classic foci in the Centre and the South of the country. L. infantum MON-24 was isolated for the first time in a small locality of Sfax (southern Tunisia) showing the appearance of a new focus of L. infantum. L. killicki was isolated in its original focus of Tataouine and in two new foci of the central part of the country (Sidi Bouzid and Kairouan).Les auteurs rapportent l’identification de souches de Leishmania isolées au centre et au sud de la Tunisie. 266 souches ont été isolées entre 1998 et 2006 à partir de l’homme (n = 221 souches) et du chien (n = 45 souches). L’identification isoenzymatique de ces isolats à permis de mettre en évidence la présence de cinq zymodèmes appartenant à trois complexes leishmaniens : Leishmania infantum, L. major et L. killicki . Tous les isolats provenant de patients atteints de leishmaniose viscérale ainsi que des chiens leishmaniens appartiennent au complexe L. infantum Seul le zymodème MON-1 est isolé de chiens ayant la leishmaniose viscérale. Cependant, il est prédominant dans le cas de la leishmaniose viscérale humaine à côté du zymodème MON-24 qui a été isolé dans deux gouvernorats du centre (Monastir et Kairouan) et du zymodème MON-80 isolé pour la première fois dans la région de Kairouan. Trois complexes sont responsables de la leishmaniose cutanée humaine : le complexe L. major zymodème MON-25 est le parasite le plus fréquemment trouvé dans les foyers classiques de la leishmaniose cutanée zoonotique du centre et du sud tunisien. Le complexe L. infantum MON-24 est isolé pour la première fois dans une petite délégation du gouvernorat de Sfax au sud tunisien montrant ainsi l’apparition d’un nouveau foyer de L. infantum . Le complexe L. killicki responsable de la leishmaniose cutanée anthroponotique est isolé dans son foyer original à Tataouine ainsi que dans deux nouveaux foyers au centre du pays (Sidi Bouzid et Kairouan) signalant le début d’extension de ce complexe