3.2.2. Influence of hold periods
If the curves for 250 °C, 350 °C and 400 °C in Fig. 4 are studied more in detail, there are ripples in the curves at regular intervals. This is the increase in peak stress registered in the cycles following right after a hold period (where a constant compressive strain was held for 30 min). It is seen that peak stresses after a few cycles go back to the trend line of previous load cycles, i.e. the following peak stress development is not much influenced. On the com- pressive side, the trough stress level is less affected, so the influ- ence on the stress amplitude is limited.