Images obtained by high-resolution X-ray tomography are used to show experimentally the three-dimensional character of short fatigue cracks in a cast aluminium alloy. The pores present in this alloy are preferred initiation sites for fatigue cracks, but no correlation can be established with the three-dimensional size of the pores. A strong interaction between fatigue cracks and grain boundaries is clearly shown, both at the surface and in the bulk, using post mortem 3D observations as well as in situ observations.

Model metal matrix composites are fabricated on purpose in this study in order to analyse damage initiation in heterogeneous metals. The materials consist in titanium matrices reinforced with SiC cylinders or aluminum matrices containing spherical zirconial/silica inclusions. The damage mechanisms of these materials are studied qualitatively and quantitatively using 3D non destructive imaging techniques (X-ray absorption radiography or tomography). In the case of the cylinders, the strain to failure of the SiC fibres as well as the interface shear strength can be directly measured. These measurements are the first attempts of direct determination of such parameters in heterogeneous materials. In the particulate composites, the strain to failure of the particles is determined using an inverse finite element calculation which validates the normal stress and stored elastic energy criteria for the rupture of the ceramic spheres.

The prolonged holding at high temperature of certain cast cobalt base superalloys may lead to rarefaction and fragmentation of the tantalum carbides which harden these alloys. Room temperature hardness, thermal dilatation and high temperature tensile strength have been studied in relation with these processes. Only the thermal dilatation coefficient and the modulus of elasticity are really affected by the evolution of the tantalum carbides.

Fe-Al alloys containing 25 and 31.5 at. % Al have been studied by internal friction, X-ray diffraction and dilatometric analyses. These techniques show for the first time that two internal friction peaks appear during the change in long range order type which occurs during the precipitation at 300°C of the metastable phase B2(FeAl). These peaks correspond to the formation of two phases: the equilibrium phase Fe3Al and a new intermediate tetragonal phase θ.

From a Finite Element analysis, the stress distribution in the notch of axisymmetric and highly loaded notched samples has been calculated. The samples are shaped like a thread root. We propose a simplified method of sizing screws for a large range of mean stresses. So, a local Haigh's diagramm at the thread root is built from the Haigh's diagram derived from smooth or notched samples.

The trapping of carbon by titanium in ferritic stainless steels with low interstitial contents depends on the presence of other non metallic elements such as phosphorus. The decrease of phosphorus content in the steels promotes the segregation of carbon at the grain boundaries and prevents the formation of the titanium carbonitrides. In fact, the formation of these precipitates depends on the quantity of remaining carbon in the matrix after the segregation of this element at the grain boundaries. Thus, this quantity could be sufficient to allow the formation of Ti(C, N) compounds by reduction of their solubility as the tempering temperature is decreased.

The part-bath heat transfer coefficient during a quenching operation is particularly important in order to simulate the workpiece hardening. The estimation of this coefficient requires specific developments in the field of instrumentation. This paper presents an experimental methodology which was developed within the laboratory. Experimental results are compared to numerical simulations using a heat transfer coefficient obtained from experimental estimation. This comparative approach allows to validate the experimental methodology and also to ensure that the tested pieces are representative.

Poly(vinylidene fluoride) (PVDF) thin films were subjected to tensile tests in plane strain over the temperature range from 65 to 115°C. At different elongation velocities using video real stress and strain, it was observed that, under such strain regimes, the neck-in starts perpendicular to the tensile axis and propagates towards the sample ends. The propagation kinetics was carefully recorded during the tensile tests. It was shown with simple hypotheses, that essential plasticity equations of the material can be determined via this method in terms of local effective stress (σeff) as a function of local effective strain (εeff) for every investigated temperature. The X-rays diffraction shows that the stretching of the sample of PVDF at a temperature lower than 72°C causes the transition from phase II to phase I.

The damage behaviour of materials depends strongly on the residual stresses generated inside the coatings realized under high energy beams. The purpose of the present work is to demonstrate the effect of intrinsic and geometrical parameters of the coated system on the stress level at the coating surface. The results of the elaborated phenomenological model show that the residual stress level depends, in particular, on the substrate and coating modulus ratio. It is then possible, based on the judicious choice of this ratio, to optimize the stress level.

On the basis of thermodynamic properties and phase diagram data, the (In,Sn) binary system was thermodynamically modelled, using the “Thermo-Calc” program of calculation. The various phases in this system were modelled with the Redlich-Kister expression for the Gibbs energies. An optimized set of thermodynamic parameters was obtained. The thermodynamic properties of the (In,Sn) binary system and comparisons between calculation and experimental data are presented.