Results 1 - 10 of 2999
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[en] Aluminum alloys are characterized by low weight and high strength but has not good mechanical properties when they are welded by electric arc with the exception of the series alloys 5XXX and 6XXX. This paper makes a review on the state of the art thermal cycling and weldability of aluminum alloys, showing the different reactions and the solidification influence that presents the cooling rate on aluminum alloys represented by curves cooling, evaluating in this way its influence on the mechanical properties of the welded joint.
[es]Las aleaciones de aluminio se caracterizan por su bajo peso y elevada resistencia mecánica, aunque no presentan buenas propiedades mecánicas cuando son soldadas mediante arco eléctrico a excepción de las aleaciones de la serie 5XXX y serie 6XXX. En este trabajo se realiza una revisión sobre el estado del arte del ciclo térmico y la soldabilidad de las aleaciones de aluminio, mostrando las diferentes reacciones de solidificación y la influencia que presenta la velocidad de enfriamiento en las aleaciones de aluminio representado mediante las curvas de enfriamiento, evaluando su influencia sobre las propiedades mecánicas de la unión soldada
[en] A series of benchmark calculations has been performed to check inelastic analysis systems used within the European Community for Fast Reactor Problems. The context and history of these benchmarks are discussed and details are given of the latest, concerning a two-bar system under cyclic thermal load and increasing mechanical load. Six analyses showed varying agreement with experiment, generally satisfactory for deformation but less good for stresses
[en] Three production Thermal Cycling Absorption Process units were each loaded with approximately 18 kg Pd/K for the Tritium Facility Modernization and Consolidation project. This report details the results of the successful loading of the units
[en] This paper investigated Incoloy 800HT (UNS N08811) alloy after some heat-cycling tests. The study continues prior tests realized in INR Pitesti concerning utilization of some nickel-based alloys in the heat exchangers and steam generators construction. The thermal-cycling consist in a successive series of heating and cooling with some rates in a range temperature. Technical parameters of thermal cycling: 50 & 200 cycles, 25 °C/minute heating-cooling rate, temperature range 450-1000°C, and argon working medium. The analysis consisted in metallographic examination (microstructure), Vickers microhardness, and traction tests. The average grain size was determined by linear interception method (ASTM E-112). The micro hardness was calculated by the relationship of the device technical book. On the Strength-Deformation diagrams were obtained: tensile strength and elongation. The tested samples were compared with the ''as received'' material. The results showed a good metallographic and mechanical behaviour of Incoloy 800HT at these thermal-cycling tests. (authors)
[en] The assessment of such stress conditions in general is made on the basis of initial cracking or ultimate load cycle curves determined by means of cyclic strain tests of small specimen subjected to single-axis loads at constant temperature. The influence of multiaxiality on the test results was verified using component-like specimen, so-called ''model bodies'', representing a turbine shaft as a geometrically scaled-down simple rotationally-symmetrical component. Using these model bodies it is possible to simulate realistic stresses (amplitude and mode, stress history), and the reliability of the transferability of small specimen results was determined on the basis of a comparison of experimental results and corresponding analytical investigations. At the same time, the range between small and large specimens was investigated in more detail using medium-size notched round specimen ( diameter 100). During all investigations it was in particular the influence of prolonged holding times on the test results that was clarified. The model body tests indicated no influence of holding times on the number of load cycles until initial cracking. Creep induced damage mechanisms were not detected by metallographic methods during the model body tests. (orig./MM)
[de]Die Beurteilung derartiger Beanspruchungszustaende erfolgt i. allg. auf der Basis von Abriss- bzw. Bruchlastspielkurven, die mit Hilfe von Dehnungswechselversuchen an einachsig belasteten Kleinproben bei konstanter Temperatur ermittelt werden. Eine Ueberpruefung des Einflusses der Mehrachsigkeit auf die Versuchsergebnisse wurde an bauteilnahen Proben, sogenannten ''Modellkoerpern'', die eine Turbinenwelle als leicht ueberschaubare rotationssymmetrische Komponente geometrisch verkleinert abbilden, durchgefuehrt. Mit Hilfe dieser Modellkoerper koennen bauteilgerechte Beanspruchungen (Hoehe und Art, zeitlicher Verlauf der Beanspruchung) simuliert werden und damit wurde auf der Basis des Vergleichs der experimentellen Ergebnisse und der zugehoerigen analytischen Untersuchungen die Zuverlaessigkeit der Uebertragbarkeit von Kleinprobenergebnissen ermittelt. Gleichzeitig wurde mit gekerbten Rundproben mittlerer Groesse ( diameter 100) der Bereich zwischen Klein- und Grossproben naeher untersucht. Bei allen Untersuchungen wurde speziell der Einfluss von laengeren Haltezeiten auf die Versuchsergebnisse geklaert. Die Modellkoerperversuche zeigten keinen Einfluss der Haltezeiten auf die Lastwechselzahl bis zum Anriss. Kriechbedingte Schaedigungsmechanismen konnten metallografisch bei den Modellkoerperversuchen nicht festgestellt werden. (orig./MM)
[en] The effect of prepoling and aging time on the dielectric properties of (1 − x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals with x = 0.33 were investigated by dielectric spectroscopy. The prepoling along the  direction induced low-temperature dielectric anomalies which disappeared by thermal cycling even within the ferroelectric phase. This suggested that the field-induced dielectric anomalies are associated with metastable states due to inherent disorder and quenched random fields in relaxors. The temporal change in the capacitance at constant temperature in the ferroelectric phase showed that the aging rate became larger with increasing temperature. It indicates that the activation barrier for the relaxation processes of polar domains and/or polar nanoregions is higher at lower temperature.
[en] Displacement instability of the thermally grown oxide (TGO) is a fundamental source of failure in thermal barrier systems. In this work, a finite element analysis has been performed to analyze the displacement instability occurring at a heat resistant metal with superficial TGO subjected to thermal cycling. Lateral and in-plane growth of the TGO which happens during high temperature is simulated by means of material property change from the substrate metal to the TGO. Most of the material properties including the TGO growth are based on the results experimentally obtained in-house. Results of the finite element analyses agree well with the experimental observation, which proves the accuracy and validity of this simulation. The technique will be useful for future work on more complicated phenomena such as deformation under thermo-mechanical cycling
[en] Conditions for realization of plane and cylindrical fronts of polymorphous transformation and the texture formed as a result of anomalous spontaneous deformation under polymorphous transformation are investigated using armco-iron samples produced by quenching with intermediate annealings and mechanical treatment. The presence of prevailing texture with <110> axis parallel to the sample axis is ascertained
[en] The fractographic study of the 12Kh18N9 steel tube fractures under thermal fatigue conditions has been carried out. Observed have been such peculiarities of fractures as: presence of three types of surface microstructure corresponding to different fracture modes and presence of several areas of fatigue fracture initiation. It has been shown that the process of thermal fatigue fracture consists of four stages
[en] The objective of this study is to investigate the reorientation of hydrides with the applied stress intensity factor, the peak temperature and the time when to apply the tensile stress in a Zr- 2.5Nb pressure tube during its thermal cycle treatment. Cantilever beam specimens with a notch of 0.5mm in depth were subjected to electrolytic hydrogen charging to contain 60ppm or 280ppm H, and then to a thermal cycle involving heating to the peak temperature of either 310 or 380 .deg. C, holding there for 50h and then cooling to the test temperature of 250 .deg. C. The reorientation of hydrides in the Zr-2.5Nb tube was enhanced with the increased peak temperature and applied stress intensity factor. Then, the reorientation of hydrides during thermal cycle had different characteristics with varying the location of the applied stress intensity under the same stress