Here, we will only briefly discuss the effect of radiation on fatigue properties. Recall the universal slopes method in Section 5.1, given by

Де = ANf 0:6 + BNf 0:12, (6.15)

where the first term represents the low cycle fatigue (LCF) that is controlled by ductility, while the second term represents high cycle fatigue (HCF) controlled

0.2 0.4 0.6 0.8

Normalized Temperature, T/TM

Figure 6.41 Effect of neutron radiation exposure on fatigue of 304-type stainless steel [35].

by strength. Now we know the constant A is directly proportional to ductility (i. e., reduction in area), while the constant B is proportional to strength (such as ulti­mate tensile strength). Since radiation exposure leads to hardening and embrittle­ment, fatigue life decreases in LCF and increases in HCF. Figure 6.41 illustrates the features clearly delineated in irradiated stainless steel tested at 325 °C, where it is noted that radiation exposure results in decreased fatigue life in LCF while improved life in HCF.

6.3