Forgeabilité des aciers inoxydables austéno-ferritiques

tel-00672279, version 1 - 21 Feb 2012
132 Chapter IV. STRAIN PARTITIONING
IV.5.2.2 Why is the overall strain different from the macroscopic strain?
IV.5.2.2.1 Question
The second question that arises from the results is the difference between the overall strain (that is to
say the average strain over the analyzed domain) and the macroscopic applied strain, see Table IV.8.
How can we account for this difference?
D1_W
D2_W
� � �
overall
�
macro
eq
Map 1
0.603
0.391
Map 2 0.809
Map 1
0.619
0.388
Map 2 0.572
Table IV.11. Differences between the applied macroscopic strain and the overall strain measured
over the analyzed fields in both D1_W and D2_W microstructures.
IV.5.2.2.2 Answer
� Back to the literature
Although the mechanics of the plane strain compression test appears rather simple, the material de-
forms inhomogeneously, the details depending upon external parameters such as the quality of tool
lubrication and the material deformation characteristics themselves. Up to recently and the paper pub-
lished by Loveday et al. [127], there was no standard for carrying out plane strain compression tests.
Mirza et al. [130, 131] wrote a series of papers in an effort to show how parameters such as material
type, specimen geometry (h0 and b0 in Figure IV.13.a), strain rate, and friction affect the macroscopic
deformation behaviour. Mirza et al. [130, 131] used extensive finite element modeling to simulate the
plane strain compression test. Two-dimensional models were adopted to reproduce hot compression
of 316L-austenitic stainless steel and aluminium and a heterogeneous strain field was observed. Fig-
ure IV.33 shows this heterogeneity of strain, strain rate and temperature on one half of the deformed
sample (the other half deforms symmetrically). It was also shown that the heterogeneity of deformation
is affected by initial geometry of the specimen but is independent of the type of material and strain
rate. In this scenario, it is essential to validate experimentally the local values of strain obtained
through finite elements modeling.
eq