Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
152 Chapter IV. STRAIN PARTITIONING
The derivation of flow properties consists of four steps: (i) image processing of a SEM micrograph; (ii)
discretization of the representative microstructure; (iii) simulating the experimental hot plane strain
compression test; and (iiii) iteratively tuning the parameters describing the constitutive behaviour of
individual phases in the FE model until a good agreement is found between the experimental and si-
mulated strain distribution.
IV.8.2.1 Image processing of the SEM micrograph
A high-resolution SEM micrograph of the undeformed sample (for instance, see Figure IV.47.a), taken
prior to testing the specimen is first chosen and subjected to the image processing in MATLAB [136],
see Figure IV.47.b. Black and white images of high contrast are desirable for this procedure so that
the two phases are clearly distinguishable. In the shown example, white colour represents ferrite and
black colour represents austenite. The image analysis algorithm reads the grey value of each pixel of
the micrograph, stores its coordinates, and computes the profile of the entire image, see Figure
IV.47.c.
a) b)
c) d)
Figure IV.47. Illustration of the microstructure modelling using sample D2_W, map2; a) SEM micrograph
of undeformed sample; b) micrograph after image processing in MATLAB [136] (black =
austenite, white = ferrite); c) geometric profile (green boundary lines computed by image analysis
algorithm; d) FE mesh, as discretized by GSMH [137].