  The main purpose of this study is to determine, via a three dimensions Finite
Element analysis (FE), the stress and strain fields at the inner surface of a
tubular specimen submitted to thermo-mechanical fatigue. To investigate the
surface finish effect on fatigue behaviour at this inner surface, mechanical
tests were carried out on real size tubular specimens under various thermal
loadings. X ray measurements, Transmission Electron Microscopy observations and
micro-hardness tests performed at and under the inner surface of the specimen
before testing, revealed residual internal stresses and a large dislocation
microstructure gradient in correlation with hardening gradients due to
machining. A memory effect, bound to the pre-hardening gradient, was introduced
into an elasto-visco-plastic model in order to determine the stress and strain
fields at the inner surface. The temperature evolution on the inner surface of
the tubular specimen was first computed via a thermo-elastic model and then
used for our thermo-mechanical simulations. Identification of the
thermo-mechanical model parameters was based on the experimental stabilized
cyclic tension-compression tests performed at 20^{\circ}C and 300^{\circ}C. A
good agreement was obtained between numerical stabilized traction-compression
cycle curves (with and without pre-straining) and experimental ones. This 3
dimensional simulation gave access to the evolution of the axial and tangential
internal stresses and local strains during the tests. Numerical results showed:
a decreasing of the tangential stress and stabilization after 40 cycles,
whereas the axial stress showed weaker decreasing with the number of cycles.
The results also pointed out a ratcheting and a slightly non proportional
loading at the inner surface. The computed mean stress and strain values of the
stabilized cycle being far from the initial ones, they could be used to get the
safety margins of standard design related to fatigue, as well as to get
accurate loading conditions needed for the use of more advanced fatigue
analysis and criteria.
