Figure 1: (A) Stress x number of cycles, (B) Strain x number of cycles,
both of the fatigue behavior presented by polystyrene.
It is noted that the graph of the number of cycles vs. stress shows a
constant behavior until fracture occurs, which was expected. However,
the same behavior was not observed in the response to tension. After the
25x103 cycle, PS acts as a viscoelastic material, and
a softening process began that may be associated with localized heating.
This is a result of the frequency employed and the low thermal
conductivity of the PS. However, no significant temperature variation (±
2 °C) was observed during equipment testing.
Many products used in industry are usually influenced by physical and
chemical conditions as well as by fatigue stress. Thus, conditions of
accelerated aging combined with fatigue stress were imposed on the PS
samples in order to discuss the relationship and the influence of both
on the material. Table 2 shows the effect of UV-B on the fatigue
behavior of the PS, under a constant load and amplitude previously
presented until total failure of the samples occurs.
Table 2: Results obtained in behavior under fatigue for all conditions.