Page 435 - Biaxial Multiaxial Fatigue and Fracture
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Cyclic Behaviour of a Duplex Stainless Steel Under Multiaxial Loading: Experiments and Modelling 419
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TANA
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Fig. 16. Comparison of model predictions and experiments in terms of equivalent stress
amplitude at the stabilized cycles with various strain amplitudes and loading paths.
Figure 16 compares the equivalent stress amplitudes given by the four models with the
experimental data at the stabilized cycles. Some tests were used for the identification (tension
path, non-proportional path at a strain amplitude of 0.5 %), the other tests were only simulated
with the identified models (torsion path, circle path at strain amplitudes of 0.2, 0.35 and
0.8 %). The same remarks as previously can be made, i.e., model NLK underestimates the
extra-hardening, models NP1, NP2 and TANA predict a stabilized Stress amplitude similar to
the experimental one obtained for the tests used during the identification. Concerning other
tests, predictions by models NP2 and TANA fit the experimental results contrary to model
NP1. Model NP1 exhibits amplitude dependent hardening under proportional path but not
under non-proportional paths. It does not accurately predict the extra-hardening dependence on
the strain amplitude applied.
In conclusion, both models NP2 and TANA are able to simulate the experimental results
observed under proportional and non-proportional cyclic loadings and at various strain
amplitudes. Nevertheless, these models are based on two opposite assumptions: the influence
of the non-proportional loadings on the mechanical behaviour is carried either on the kinematic
component or on the isotropic component. The study of the macroscopic mechanical behaviour
is then inadequate to identify the strengthening components concerned by the extra-hardening.
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CONCLUSION
A large series of uniaxial and biaxial tests were carried out on a forged duplex stainless
steel. These tests bring out some characteristics of the mechanical behaviour of the duplex
stainless steel: the cyclic behaviour is isotropic, whatever the loading path the steels shows a
