Figure 7. Regions for showing plastic and creep zone
The effect of the load ratio (R ) and hold time (th ) on the plastic zone size are shown in Fig. 8. The contours in Fig. 8 indicates the plastic zone where the equivalent plastic strain is greater than 0.2 %. Both at initiation (Δa = 0 mm) and growth (Δa = 2 mm), the plastic zone size is dependent mainly on the load ratio, whereas the hold time effect is minimal.
Corresponding results for the creep zone size are shown in Fig. 9. The contours in Fig. 9 indicates the creep zone where the equivalent creep strain is greater than 0.2 %. At initiation (Δa = 0 mm), the creep zone size under tension-compression loading (R < 0) is much smaller than that under tension-tension loading (R > 0), and the creep zone size becomes larger with the longer hold time. The same tendency is observed at crack growth (Δa = 2 mm), but the effect of the load ratio becomes weaker and the effect of the hold time is more dominant than that of the load ratio at crack growth.