Page 436 - Biaxial Multiaxial Fatigue and Fracture

420 V AUBIN, P QUAEGEBEUR AND S. DEGALLAIX

cyclic hardeningkoflening and an extra-hardening occurs under cyclic non-proportional
loadings.
a As austenitic stainless steels, the duplex stainless steel is sensitive to loading path,
although the extra-hardening observed is lower for the duplex stainless steel. Three goups of
loading paths are distinguished with increasing stabilized stress responses: (1) tension-
compression, torsion and proportional 45" paths, (2) clover path, (3) square, circle and
hourglass path.
Four sets of constitutive equations were selected (NLK, NPI, NP2 and TANA) and their
material dependent parameters were identified on the data base,
The comparison of the test results and the simulations clearly shows that two models
(NP2 and TANA) are able to accurately predict the experimental observations.

The both models selected are based on two opposite assumptions about the strengthening
components. The macroscopic tests carried out do not allow to identify the most realistic
assumption and to connect the macroscopic behaviour to a physical meaning. Supplementary
tests are needed to bring out strengthening components involved in the extra-hardening and the
way they affect it. These necessary pieces of information can notably go through the
measurement of the evolutions of variables X and R during non-proportional cyclic tests.

ACKNOWLEDGEMENTS

The authors are grateful to FEDER and the Nord-Pas-de-Calais Region for their financial
support in the purchase of the biaxial equipment.

REFERENCES

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