Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
Chapter IV. STRAIN PARTITIONING 151
IV.8 Perspective: derivation of per-phase flow properties
IV.8.1 Introduction
The published literature indicates that the accommodation of macroscopic deformation of DSS de-
pends on the plastic characteristics of both phases [25, 29, 48] and the interface [9, 12, 95], as well as
the morphology of the two phases [11]. The results of this work confirm and complete the published
results. However, lack of accurate information of flow properties of individual phases makes it chal-
lenging to clearly understand the damage mechanisms taking place at the interface. As a conse-
quence, deformation models should be developed based on the microstructures analyzed experimen-
tally by the microgrid technique in order to determine the flow properties of the individual phase. This
modelling effort is currently undertaken by co-workers: Sampath Kumar-Yerra et al. [134, 135] at the
University of Louvain-la-Neuve in Belgium. The objective of this section is to briefly present the strat-
egy used to derive the flow properties of the individual phases, and to give some results based on one
example. The purpose is to show that this strategy allows a systematic approach to determine the
contrast in terms of plastic properties between both phases. The finite element (FE) analysis has been
used to study the macroscopic mechanical behaviour of DSS in rolling process and in hot plane strain
compression [16, 125]. In this work, the technique is used to compute the flow properties of the indi-
vidual phases. The adopted approach mainly relies on reproducing through FE modeling the experi-
mentally determined micro-scale strain distribution in the two phases of a DSS sample subjected to
hot plane strain compression test. Two levels of information can be extracted from the microgrid expe-
riments: average strain per phase and strain maps showing complete strain distribution i.e., with in-
formation of the strain tensor at every microgrid intersection.
IV.8.2 Microstructure modelling
The principle involved in the modeling strategy is schematically shown in Figure IV.46. The various
aspects of it are explained and illustrated with an example below. The chosen duplex stainless steel
sample is the D2 alloy with a Widmanstätten morphology. This sample was deformed at 850°C and 1s -
1 applying a 30% thickness reduction.
Image Processing
(MATLAB)
Mesh Discretisation
(GMSH)
Propose two guesses
per each flow
parameter Pi
64 simulations of
mechanical test
(ABAQUS)
Extract Strains and
choose optimal guess
for all Pi corresponding
to the least Residual
Is Residual
decreasing?
DONE!
Figure IV.46. Schematic of the modelling strategy for identification of the phase properties properties.
i = 1
No
Make next guess
for parameter Pi
Simulation of
mechanical test
(ABAQUS)
No
i = i + 1
Is i= imax?
Yes
Yes