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.