No abstract available

[en] A new experimental method for the investigation of stress corrosion cracking mechanisms in thin sheets is presented: Using the foil penetration technique, the growth kinetics of the intergranular corrosion of age-hardened Al-Cu alloys have been measured in the unstressed condition and under various constant uniaxial tensile stresses. A pure binary Al-4wt%Cu alloy and a commercial AA 2024 alloy, both tempered to maximum susceptibility to intergranular corrosion, have been tested in aqueous chloride solutions under potentiostatic control. All measurements have been carried out on various sheet thicknesses between 0.2 and 1.0 mm under tensile stresses ranging from 0 to 88% of the 0.2% proof stress. A significant reduction of the penetration times by factors between 2 and 10, compared to the results for unstressed specimens, has been observed for all applied stress levels in systems where only small numbers of cracks are growing simultaneously. In systems with large numbers of cracks or complete crack networks, no influence of stress on the crack growth kinetics was found. The discussion of these results shows that all, even the highest observed mean crack growth rates can be explained by pure anodic dissolution of the grain boundary regions at the crack tips. The increase of the dissolution current density at the crack tips by tensile stresses is due to the widening of the crack, which reduces the integral ohmic resistance of the system and improves the mass transport conditions between the crack and the bulk electrolyte. The widening of the cracks depends on the stress distribution in the whole specimen cross section and not on the stress intensity at the crack tips. 23 refs., 14 figs., 1 tab

[en] Titanium nitride (TiN) coatings, produced by physical (PVD) or chemical (CVD) vapor deposition techniques are used routinely to improve the wear and corrosion resistance of a surface. The main problem in using TiN as a protective coating in aggressive environements are pores and pinholes in the coating where the substrate is exposed to the electrolyte. In this work, the electrochemical and corrosion behaviour of TiN films on quartz glass, carbon steel, 304 and 316 stainless steel is studied by polarization curves and electrochemical impedance spectroscopy (EIS) in hydrochloric acid. It is shown that the TiN coating can be used successfully only on substrates that passivate easily. On mild steel rapid corrosion takes place at pores in the coating due to the very noble steady state potential of the TiN coating. The interaction of the metallic substrate with the TiN coating is discussed for the two limiting cases mild steel (active) and 316SS (passive). It is shown that the determination of the coating porosity is possible for the active substrate only. On the passive substrate the occurence of an additional time constant in the high frequency region of the spectrum qualitatively indicates the presence of pores. A quality control of the coatings based on this fact might be possible. (author) 15 refs., 6 figs., 2 tabs

[en] The following tables list the values of the atomic ionization cross sections. Calculations have been performed considering the two fundamental theoretical approaches to the ionization process by heavy charged particles collision, i.e. Plane Wave Born Approx. (P.W.B.A.) (quantistic model) and Bynary Encounter Approx. (B.E.A.) (semiclassical model). The most significant corrections of both models have also been considered

[en] The paper describes a sampling methodology to be followed in a mixed-oxide (MOX) fuel fabrication plant where a continuously updated computerised nuclear material management system is available, assuming that access is granted at all points of the plant. The present methodology considers that a finite number of repetitive verification activities, spread over the detection time period, will be performed. Sample sizes for the activities are determined, under relatively broad conditions, assuming cluster sampling so that the inspection goals will be reached without stopping the fabrication process once a month as required at present. (author)

[en] This paper deals with the problem of checking medium-size families of items of similar specification during inventory verifications. An example of quantitative analysis using the signed rank test is given. The hypotheses commonly accepted in the statistical tests performed are extensively discussed. The difficulties met in practice which limit the application of the theory are pointed out and the solution adopted in the case considered is illustrated. (author)

[en] In a previous work the authors proposed, in the frame of the binary-encounter approximation (BEA) of the inner-shell atomic ionization by ion bombardment, a correction to the ion energy in order to account for the Coulomb repulsion by the atomic nucleus. Such corrected cross-section values numerically coincide with those of the PWBA model, but, as a consequence of the correction, they obtain a much higher-energy ionization threshold than the binding energy, which has no experimental evidence. In the present work it is shown that ionization below such a threshold can be explained by a double-collision mechanism which involves intermediate electron states and can directly be derived from the impulsive nature of the binary-collision model. Calculations have been performed by supposing a statistical independence between these two collisions. Relativistic corrections have not been taken into account. A remarkable agreement is obtained between the curves corresponding to single- and double-collision classical processes, since they match at the bombarding threshold ion energy. (author)

No abstract available

[en] 1 - Nature of physical problem solved: Measurements of in-pile fast neutron spectra are often obtained by threshold detector irradiations. The threshold detector technique gives data usually expressed as normalized activation rates. The programme RDMM allows the energy dependent flux determination, on the hypothesis that the neutron flux shape can be expanded in a series of linearly independent functions times a weighting function. Moreover it allows to estimate the effect of experimental input errors on the solution obtained. 2 - Method of solution: The series expansion coefficients are obtained through the Gauss method by solving a least-squares problem. A procedure based on the Monte Carlo method is used to statistically study the effect of experimental errors

No abstract available