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In the present paper, a synthesis of the relations between diffraction stress analysis
and multiscale modelling is presented. It is found that, although models give good
qualitative and quantitative results in the elastic field, the extension to internal
stresses of elastic-plastic origin remains semi-quantitative and many studies are still
required to obtain a consistent formulation between diffraction and modelling.
The determination of residual stresses and the analysis of phases in
zirconia layers obtained after oxidation of Zy-4 and Zr-1%Nb-O sheets have been
performed using X-ray diffraction with synchrotron radiation at 20 and 400°C.
These experimental analyses have been compared with calculations using a
micromechanical approach (thermoelastic behaviour) and also with a macroscopic
approximation of the thermal stress due to cooling. The main result is the small
influence of cooling on the residual stresses developing in the zirconia layer,
especially for Zr-1%Nb-O.
A self-consistent elastic-plastic model has been developed for the analysis
of the behaviour of rolled samples of zirconium 702 during mechanical loading.
The thermal residual stresses produced by cooling from the annealing temperature
to room temperature have been determined and compared to X-ray diffraction results.
The elastoplastic behaviour of zirconium in tensile tests along the rolling and
transverse directions has been simulated and compared to the experimental results.
The influence of texture and of existing thermal stresses on the response of the material
could be studied and explained by this approach.
In this study, we present an analysis of the internal stresses generated
during cooling of alumina-chromium composites using a micromechanical approach
by a finite element method. Residual stress fields are calculated for microstructural
models derived from a scanning electron microscope image. Results show in particular
that particles with concave shapes can generate relatively high local plastic
deformation and residual stress distributions in the adjacent matrix that are very
different from those of particles with a spherical shape. We present also the experimental
determination of residual stresses using synchrotron radiation from LURE. We show that
measurements are possible and the results concerning the mean stresses in the alumina
and chromium phases are analyzed.
Homogeneity methods are very helpful in the interpretation of X-ray line
shift and broadening. The use of self-consistent models becomes general, but the
information given by these models, which is shown to be strongly linked with diffraction
measurements, can not yet be completely exploited. It is in particular shown that the
intra-phase heterogeneity of strains should in certain cases be reflected by the line
A phenomenological relation is proposed for the description of the mechanical
behaviour of Zr 702α polycrystalline samples deformed in channel die compression
at room temperature. The identification of the parameters of the model from macroscopic
stress-strain curves shows a good description of the anisotropy of the material.
The analysis of the identified parameters shows the role of the activated deformation
modes in the different samples.
In multiphase materials, X-Ray Elasticity Constants (XEC) depend on the nature
and volume fraction of each phase constituting the polycrystal. These XEC play a
leading role during X-Ray diffraction stress analysis. Self-consistent scale transition
models have been developed in order to simulate the XEC characteristics of several
two-phase alloys. This work makes possible the quantitative study of the influence
of the second phase on the results of X-Ray stress analysis.
The impregnation of a fibrous preform by a liquid metal is one of the techniques
used to prepare metal matrix composites (MMC). The preparation by impregnation may
however lead to defects like microporosity. The micropores present in MMC result from
the superposition of two processes: the trapping of gas by capillarity during the
infiltration phase and the formation of additional porosity related to solidification
shrinkage. These two processes are analyzed in this paper and physical models are
proposed for their description. It is then shown how the formation of microporosities
can be simulated numerically using these models. Finally, prospects for a better numerical
simulation of the preparation of MMC by impregnation are discussed.
This study concerns the influence of certain metallurgical factors, like the addition
of a mixture of rare earth metals (mischmetal) and of overheating, on the microstructure
and the tensile properties of alloy A319-2 (Al-Si-Cu with 0.4, 0.8 and 1.2% iron)
The new phase linked with mischmetal has a needle - and/or platelet - shape as
the β-iron phase and impedes the flow of the liquid metal during casting, thus
creating porosity. The different types of particles present in the microstructure
remain after the T6 thermal treatment. In the alloys containing 1.2% iron,
the length of the β phase and mischmetal particles is slightly smaller than in the
alloys with 0.4% Fe or 0.8% Fe, after the addition of 5% mischmetal and
overheating at 950°C. This explains the better tensile elongation of the
1.2%Fe-5% mischmetal alloy cast at 950°C instead of 750°C. UTS and yield
strength are decreased by the addition of mischmetal but are slightly improved
by overheating. Overheating at 950°C decreases the yield strength only
in the 1.2% Fe-0% mischmetal alloy.
The multiplication of magnetic domain walls under the effect of induced
currents developed during high frequency magnetization loops is experimentally
investigated in ultra-soft nanocristalline alloys in order to determine the effective
anisotropy and to check the predictions of the Random Anisotropy Model used to explain
their extreme softness. For the first time, direct observation of multiplication is achieved
and resulting effective anisotropy determinations underline the importance of induced
anisotropy upon effective anisotropy.
The corrosion resistance of two aluminium alloys, 6063 and 3003, has been compared
using a 0.5 M sodium chloride solution. The results obtained with electrochemical
and metallographic techniques show that alloy 6063 is more resistant than alloy 3003
at 25°C. The corrosion rate tends to increase as the pH deviates from neutrality.
When the chloride concentration is decreased, the resistance to pitting corrosion
is improved for both alloys. The influence of the temperature of the medium on the behaviour
of the two alloys has also been studied. In the case of alloy 3003, the corrosion
rate (Icor) increases with temperature up to 55°C, but drops back to its room
temperature value at 65°C. In the case of alloy 6063, Icor decreases
as temperature is raised up to 65°C. At all testing temperatures, the 6063 alloy
has a better corrosion resistance than the 3003 alloy.