DEFORHATION TEXTURES CONNECTION BETYEEN NODELLIN AND EXPERIENCE IN ELASTOPLASTIC BEHAVIOUR OF POLYCRYSTALS

The general framework of this contribution can be described as follow a) a-brass the classical mechanical tests such as uni’axial tension along the transverse and rolling direction, biaxial tension and close to plane-strain deformation are performed. b) aluminium the influence of a prestrain is studied in the case of complex loading pathes. c) quantitative measurements of the initial and deformation textures are realized using either X-ras or neutron diffraction. d) an attempt is made to reproduce the deformation textures by modelling the anisotropic behaviour of polycrystalline materials in the framework of a self consistent scheme.

The general framework of this contribution can be described as follow a) a-brass the classical mechanical tests such as uni'axial tension along the transverse and rolling direction, biaxial tension and close to plane-strain deformation are performed. b) aluminium the influence of a prestrain is studied in the case of complex loading pathes. c) quantitative measurements of the initial and deformation textures are realized using either X-ras or neutron diffraction. d) an attempt is made to reproduce the deformation textures by modelling the anisotropic behaviour of polycrystalline materials in the framework of a self consistent scheme.
2") INITIAL STATE, MECHANICAL TESTS AND TEXTURES a) a-brass specieen the sample is a cold rolled strip with nternedate and final annealing. The grains are approximatively equiaxed but with mxed grain szes (dameters between 25 and 5 m).
The yield locus of the a-brass has been determined using the uni-1115 1116 F. ROYER ET AL axial tensile test, baxial expansion (bulge test) and a specific geometry of the sample which allows to involve simultaneouly close to plane-strain deformation and uniaxia] tension [ 1,2 ]. The principal results obtained are the following the baxal flow stress appears greater than the average uniaxial stress even though the Lankford's coefficient is less than one plane-strain flow stresses e.ther in rolling or transverse directions are greater than in uniaxial tension at low strains. Increasing strain mples that flow stresses under unaxial or plane-strain become very similar under unaxial tension the flow stress along the transverse direction has a greater rate of hardening then along the rolling drecton.
These results and the summary of all the results concerning other loading pathes lead to the fact that a description of anisotropy by currently proposed yeld criteria [ 3,4 ] s not sufficient for Q-brass. So the question can be asked on the nature of the nformatons that can be put out from texture measurements.
Because of the geometry of some deformed samples and for the precision of the measurements, textures have been determined by neutron -diffraction on a chanel of the nuclear reactor of Saclay. b) aluminium 15% sheet in a second set of experiences, uniaxial tensile tests along the rolling and transverse directions are performed on a material with a sharper texture as the previous one. Furthermore the influence of a predeformation is studied in the framework of a combination of tensile tests in the rolling direction plus transverse direction and vice-versa. In this study too a particular geometry of the test sample [ 5 ] is used. Once more the importance of the crystallographic texture evolutions can be pointed out: [6] the initial texture is described by two components, For higher strains, the pecularities of a RD tension appears. prestain # TD + tension # RD the texture obtained is typically the one developped during the second path on and after the first RD strain.  Table 1 presents the Taylor's factors for the a-brass sample. From a textural point of view one may conclude that the flow stress in uniaxial tension along TD is greater than the corresponding one along RD in deformed states.
The hardening strain rate in plane-strain is lower (slightly higher in baxial expansian) than n uniaxial deformation. Always in the framework of the Taylor's model, a qualitative analysis of the yield loci obtained for the aluminium sample does not show drastic differences.  results, t appears that the basis set does not contains enough nformatons to describe wth a good accuracy the initial texture. 4")CONCLUSION.
The importance of the crystallographic texture in the description of the anisotropy of polycrystals is clearly pointed out is this contribution. The fundamental interest for complex loading pathes has to be seriously developped because of the large amounts of results that can be obtained concerning the development of textures during industrial processes. The choice of a basis set including all the informations of the initial texture has to be discussed.