[en] The first results of the differential cross sections of elastic αd scattering at 3.98 GeV/c have been measured over a range .08<-t<1.8(GeV)². In this experiment the incident α-particles beam extracted from the Saclay Saturne Synchrotron hits a liquid deuterium target and only the secondary α-particles are analysed by means of an achromatic double focussing spectrometer. For /t/>.2(GeV)², the experimental data on αd collisions exhibit a two-peak structure in the secondary alpha spectra which corresponds to elastic and quasi elastic (with target deuteron break up) αd scattering. The quasi elastic parts of the spectra are analysed within the framework of the Glauber multiple scattering model. The values of the differential cross sections for elastic αd scattering are determined by substracting the quasi elastic contributions given by the theoretical calculation. The obtained differential cross sections which clearly show the first and second diffraction minima, are compared with three models generalizing the multiple scattering theory to nucleus nucleus scattering. These models use simple gaussian nuclear densities without short range correlations and approximate the nucleon nucleon scattering amplitudes with a simple exponential dependence according to the optical theorem. The prediction of CZYZ and MAXIMON model are the only ones to describe successfully the variations of the αd elastic differential cross section over the range of investigated transfers

[en] Zirconium shaping requires various methods: forging, extrusion, rolling, stamping, folding. The last method is retained as acceptance test for plates. Main parameters affecting bending are studied with tests and numerical simulations. The spring-back at the end of bending and optimal annealing temperature are also examined

[en] In fast reactors the mixture of sodium at different temperatures is a source of thermal striping that can produce crack growth on metallic structure in the neighborhood. The aim of this study is the determination of conditions for crack formation at the surface of stainless steel components by heat. Testing equipment reproducing superficial thermal fatigue was realized and first tests concerning metallographic observations and microfractography are presented. Crack initiation is constituted by a great number of microcracks below 50 microns and their orientation are dependent of main plastic deformations. During crack propagation longer cracks (up to 3 mm) form a tridimensional network, characteristics are the same for mechanical and thermal fatigue

[en] Dissimilar ferritic-austenitic welded joints present in several nuclear reactor components are frequently subjected to fatigue. In this context we have measured the fatigue crack growth rate in a ferritic-austenitic welded plate using compact tension specimens. The most significant observation made is an important decrease of the crack propagation rate, linked to a high level of crack closure when cracks reach the ferritic-austenitic boundary. The reason for this is shown to be the presence of high residual stresses produced during the welding operation. Measurement of these stresses are made using a hole drilling method modified to allow determination of non-uniform stress fields. This method is based on the existence of a special function called transmissibility function. From the stress measurement results, first the residual stress intensity factors are derived using a weight function method and then a quantitative crack propagation analysis is performed. The results obtained give a satisfactory explanation to the observed decrease in the crack propagation rate and the crack closure phenomenon

[en] Strength to the fracture of the pipe in PWR has to be justified with mechanical analyses. These tests are based on the strength to ductile fracture of steels which are tested in lab. The values of resistance to fracture are obtained through tensile tests on CT specimens (determination of J-R curves). The purpose of this study is to justify the sizes of the specimens which have to be used to characterize the strength to ductile fracture of steel in secondary pipes. Tests were conducted on 0,5T-CT, 1T-CT and 2T-CT specimens. Two materials with different suffer contents were studied. The test results show that the JO,2 values gotten from the different specimens are similar. But the strength to ductile fracture in 2T-CT specimens in lower than the one measured in 0,5t-CT and 1T-CT specimens. The surface of fracture of the different specimens displays splits perpendicular to the notch and parallel to the sheet surface. These splits are produced by the separation of the manganese sulfur inclusions. The effect notes on the J-R curves seems to be relevant to these splits. The reason why these splits might be responsible for a decrease of the tearing modulus are not clearly defined up to this point. The results which have been published show the importance of the geometry effects (presence or not of lateral notches...) and the loading mode on the strength to ductile fracture. We note that the curves determined from tests on CT specimens are conservative. A few preliminary studies showed that the geometry effects on resistance to fracture can be studied and explained by using local approach methods. The Rousselier modeling is useful to explain the behaviour of ferritic steels in ductile fracture. (authors). 20 refs., 7 figs., 5 tabs

[en] This study deals with the effect of loading path on the strain to failure of a C-Mn-Ni-Mo steel. The tests are carried out at 373 K on axisymmetric, notched tensile specimens calculated by the finite element method. Specimen geometries containing different notch radii and leading to widely different stress triaxiality ratios are investigated. The effect of nonradial load path is studied using relatively sharply notched specimens. It is shown that a simple linear damage rule does not account for the experimental results. A model based on the critical cavity void growth rate calculated from the Rice and Tracey model is shown to give results consistent with the experiments provided that the effect of prestrain on constitutive equation and on the stress triaxiality ratio is properly taken into account. The experimental results are also compared to a model based on continuum damage mechanics. (author)

[en] Tensile tests were performed on homothetic different sized axisymmetrical notched tensile specimens (NT), at 100 C. A strong size effect was observed on the ductility : The average strain at fracture, as well as the scatter of results, decrease with the size of the specimen. Two statistical methods are proposed to model this size effect. The first modelling is a continuous approach based on mechanics of porous material, on a distribution of manganese sulphide volume fraction in a representative volume elements (R.V.E.) and on the weakest link theory. The second one is a discrete approach based on a Monte Carlo randomisation of critical growth rate of voids in finite element calculation. These two models are in agreement with the experimentation. In both cases, the size and scatter effects are obtained by the dispersion of the chosen intrinsic variable, as well as by the relative dimensions of the R.V.E. and of the whole specimen. The discrete approach shows a larger variation of the scatter than the continuous one. In particular, the saturation for large volume seems to be better described by the discrete approach. However, in the continuous approach, the introduction of an upper bound in the statistical description of the manganese sulphide fraction leads to an accurate description of the saturation effect. (orig.)

[en] The evaluation of the reliability of pressure vessels in nuclear plants relies on the evaluation of failure probability models. Micromechanical approaches are of great interest to refine their description, to better understand the underlying mechanisms leading to failure, and finally to improve the prediction of these models. The main purpose of this paper is to introduce the stress heterogeneities arising within the polycrystal in a probabilistic modeling of brittle fracture. Stress heterogeneities are evaluated from Finite-Element simulations performed on a large number of Statistical Volume Elements. Results are validated both on the measured averaged behavior and on the averaged stresses measured by neutron diffraction in five specific orientations. A probabilistic model for brittle fracture is then presented accounting for the carbide distribution and the stress distribution evaluated previously inside an elementary volume V₀. Results are compared to a 'Beremin type' approach, assuming a homogeneous stress state inside V₀. (authors)

[en] Experimental results are presented concerning the influence on zirconium 702 rupture properties, of various metallurgical and mechanical parameters such as: microstructure type, initial strain hardening rate, anisotropy and stress direction, oxygen content in welds

[en] The aim of the present work is to derive empirically a simple expression of the uncertainties on Charpy transition temperatures (TT), which depends only on the test temperatures and the number of tests at each of these temperatures. Calculations of the TT uncertainties of a RPV steel are performed based on an empirical representation of Charpy test results and a Monte Carlo procedure to generate large numbers of data sets for different test matrices. Applying usual procedures to determine the TT to the generated data sets gives access to the distributions of these quantities from which the uncertainties are calculated.An analytical expression for these uncertainties is proposed. (author)