An assessment of the θ-projection method for the representation and extrapolation of creep data for a 1%Cr, 12%Mo, 14%V steel tested at 565°C

Constant stress creep data for a wrought 1%Cr, $\text{1}\text{2}\text{\%}\text{Mo}$, $\text{1}\text{4}\text{\%}\text{V}$ steel obtained from six tests carried out at 565°C have been fitted and extrapolated using the θ-projection method. Creep curves for high stresses were fitted well, but curves extrapolated to stress levels below those used in the θ-projection did not represent well the available data for primary-secondary creep. To enable a satisfactory extrapolation of results, it was found necessary to redefine the failure condition to be less sensitive to the shape of the latter sections of the tertiary creep curve. This was achieved by defining lifetime as the point on the curve at which the strain rate reached a fixed multiple of the creep rate at half the rupture time. The extrapolated data compare well with the results of tests carried out independently on a cast 1%Cr, $\text{1}\text{2}\text{\%}\text{Mo}$, $\text{1}\text{4}\text{\%}\text{V}$ steel. The extrapolation procedure not only predicts the ‘knee’ in the log stress-log lifetime curve but allows extrapolation of lifetimes by over a factor of thirty. In addition, acceptable predictions have been made of constant load experimental data.     

Oxydation catalytique des phenols par le peroxyde d'hydrogene: Etude structurale des catalyseurs Fe/Al2O3 et Fe-Cu/Al2O3 par spectroscopie Mossbauer

This study recalls the results obtained on the oxidation by hydrogen peroxide of a number of hydroxyl aromatic compounds with alumina supported catalysts and more particularly the structural study of these catalysts. The catalysts were prepared under different conditions: without thermic treatment, by oxidation in air at 450°C and by thermic reduction at 500 and 700°C, under hydrogen flow. The structural study by Mössbauer spectroscopy of the catalysts Fe/Al₂O₃ and Fe-Cu/Al₂O₃ made it possible to specify in what form was found the iron, as a function of the conditions under which the catalysts were prepared. For the catalyst prepared by impregnation without thermic treatment the iron on the support was in hematite form (α-Fe₂O₃) well crystallized in small particles with 10–20% iron which could be ferric ions (Fe³⁺) chemically adsorbed on alumina or iron within the structure of the alumina (Figs 7 and 8). Thermic oxidation in air brought about the appearance of hematite in the form of large particles (Fig. 9) whereas the thermic reduction under hydrogen flow led to the formation of crystallized metallic iron (α-Fe) (Fig. 12). The reducibility of iron on the support increased with the increase in temperature of reduction and with the presence of copper (Figs 11 and 13). As for the activity of the different catalysts in oxidation reactions of phenols by hydrogen peroxide, we notice that whatever the form of the catalyst, the activity was more important for pyrocatechol than for phenol (Fig. 3). As far as stability of the metals on the support was concerned, during the oxidation reaction we noticed that it was greater with an oxidized catalyst than with a reduced one (Figs 4 and 5). The comparison between the results obtained in a batch and in a continuous reactor made it possible to show that the first phase of the reaction was probably due to the superposition of the phenomena of homogeneous (by the Fe ions passed into solution) and heterogeneous catalysts (Fig. 6). The comparative structural study reduced before and after use was quite in agreement with the solubilization of iron that we observed during oxidation (Figs 15 and 13). However on the oxidized catalyst hematite was not modified after use and the most significant change on the spectrum was a slight decrease of E_Q (0.1 mm s^?1) in the central doublet (Figs 14 and 9).     

Formation of cube texture in nickel-palladium alloys for epitaxial substrates for deposition of high-temperature superconductors

The texture, structure, and magnetic and mechanical properties of thin ribbons of nickel-palladium alloys have been studied. It has been demonstrated that in Ni₉₄Pd₆ and Ni_92.5Pd₅W_2.5 alloys, a sharp cube texture can be formed that is stable up to rather high annealing temperatures. Segregation of palladium atoms to surface layers of ribbons has been found, which gives additional advantages for using these ribbons as substrates for epitaxial deposition of high-temperature superconductors.     

Surface tension isotherms of a free surface and grain boundaries in the Cu-Sn system

Surface tension of pure copper and its alloys with Sn has been measured at 1000°C in a hydrogen atmosphere. Surface tension of a free surface equaled 1.81 N/m for pure copper, and 1.55, 1.38, and 1.28 N/m for the alloys with 0.05, 0.22, and 0.33 at % Sn, respectively; surface tension at grain boundaries equaled 0.5 N/m for pure copper, and 0.36, 0.3, and 0.23 N/m for the alloys, respectively. Based on these data, the concentration dependence of tin absorption at a free surface and grain boundaries has been calculated. Parameters of Sn absorption at grain boundaries and a free surface of copper have been compared with those of Sb and Bi.     

A Review of Dynamic Fracture Studies in Functionally Graded Materials

Abstract:  This article presents a review of dynamic fracture studies on functionally graded materials. A brief literature review on the fracture mechanics of graded materials is presented first. This is followed by a discussion on the higher-order asymptotic analysis of the transient elastic field surrounding the tip of a dynamically growing crack in a functionally graded material. A comprehensive experimental study of dynamic crack growth in model functionally graded material using the optical method of reflection photoelasticity and high-speed photography is then presented. The results are analysed to establish a generalised relationship between the crack velocity and the dynamic mode-I stress intensity factor (SIF). This relationship is found to be unique and is distinctly different from that previously established for the matrix material (polyester). Finally, an innovative experimental procedure is used to demonstrate the necessity of employing a fully transient stress-field representation in the analysis of optical data for an accurate prediction of the dynamic SIF history.     

Impedance spectroscopy of ultrafine-grain SnO2 ceramics with a variable grain size

The impedance spectra of nanocrystalline SnO₂ ceramics with an average grain size d ranging from 3 to 43 nm were investigated in the frequency range 1–10⁶ Hz at temperatures from 25 to 300°C in a dry oxygen atmosphere. Analysis of the experimental data by the graphoanalytical method made it possible to separate the contributions of grain bulk and grain boundaries to the conductivity. It is shown that the samples investigated can be arbitrarily divided into two groups with respect to the character of their conductivity. For the samples with an average grain size d < 25 nm, the charge transfer processes are almost completely determined by the grain boundaries. In samples with a larger grain size, the contribution of grain bulk to the conductivity is comparable with that of grain boundaries.     

Development and adoption of measures for increasing the safety of power-generating units of nuclear power plants with RBMK reactors in 1986–2005

The basic stages and directions of upgrading and reconstruction of the power-generating units of nuclear power plants with RBMK reactors over a period of 20 yr since the Chernobyl accident are reflected in this paper. The greatest amount of work was done in 1986–1990 on all units with RBMK-1000 and-1500 reactors which were operating at that time in the USSR. The purpose of the upgrade was to improve the neutron-physical characteristics of the reactor cores, increase the response speed of the safety and control system and decrease the positive effect of water outflow from the cooling loop of this system, increase the flow capacity of the systems performing emergency discharge of the steam-gas mixture from the reactor, and improve the basic operating documentation. The subsequent stages of the upgrading and reconstruction concerned mainly the first-generation power-generating units (Nos. 1 and 2 units of the Leningrad and Kursk nuclear power plants). These works were performed to make the power-generating units conform to the requirements of the modern normative documents on safety and allow for the possibility of these units to remain in operation after the nominal 30-yr service life has been exhausted. __________ Translated from Atomnaya énergiya, Vol. 100, No. 4, pp. 312–320, April, 2006.