Font Size: 

The energy dissipated to the surroundings as heat in a unit volume of material per cycle, Q, was
recently proposed by the authors as fatigue damage index and it was successfully applied to correlate fatigue
data obtained by carrying out fully reversed stress- and strain-controlled fatigue tests on AISI 304 L stainless
steel plain and notched specimens. The use of the Q parameter to analyse the experimental results led to the
definition of a scatter band having constant slope from the low- to the high cycle fatigue regime. In this paper
the energy approach is extended to analyse the influence of mean stress on the axial fatigue behaviour of unnotched
cold drawn AISI 304 L stainless steel bars. In view of this, stress controlled fatigue tests on plain
specimens at different load ratio R (R=-1; R=0.1; R=0.5) were carried out. A new energy parameter is defined
to account for the mean stress effect, which combines the specific heat loss Q and the relative temperature due
to the thermoelastic effect corresponding to the achievement of the maximum stress. The new two-parameter
approach was able to rationalise the mean stress effect observed experimentally. It is worth noting that the
results found in the present contribution are meant to be specific for the material and testing condition
investigated.