The average values obtained in this study clearly show that the cyclic
stresses and the exposure to UV significantly influenced the mechanical
properties of PS, presenting a relative dispersion characteristic when
dealing with fatigue. Thus, the useful life (number of cycles to
failure) of the irradiated PS was less than that of the as-received PS,
with a reduction of 45% for 336 h of exposure, corresponding to an
energy of 24.1 MJ/cm2. A reduction of 51% for 575 h
of exposure was observed, which corresponds to almost twice the energy
of the previous result, 41.2 MJ/cm2. This indicates a
weakening of the irradiated material, as highlighted in Figure 2.A.
Cyclic loading under tension control does not have a constant strain
range. In this study, it was observed that the material resistance to
cyclic deformation increases with the fatigue process, in addition to
presenting an exponential behavior. Therefore, in order to
quantitatively evaluate the behavior of the material regarding
softening, the relationships between the onset of this phenomenon with
respect to the number of cycles (Figure 2.B) and cyclic deformation
(Figure 2.C), both depending on the exposure time, were performed and
noted during the test.
The results obtained in the tests show that the softening process occurs
after half the useful life of the material with 53% for PS under
fatigue, 72% for PS fatigued and exposed to radiation for 336 h, and
80% for PS fatigued and exposed to radiation for 575 h.