Y. Miyashita et al. /International Journal of Fatigue 24(2002)241-248 (c)Type 2 Fig. 7. Schematic illustrations of crack growth processes. materials, the variation in MOR, as has been previously figure that the MOR reduction decreases with increase in suggested [10-12], was used in this study. The mOR was the total crack length. It is also noted that in some cases calculated from stress-strain hysteresis loops, which were the MOR increased with crack growth at low stress levels ecorded during fatigue tests. The MOR was taken to be(Fig. 10(a)). This anomalous behavior was observed for the slope of the unloading curve between the maximum all types of crack growth processes. Initial MOR, final stress and 10% of the maximum stress. the variation of mor and maximum mor are shown in fig. 11. values the mor reduction and of the total crack length with of the maximum mor are larger than the initial mOR increasing number of cycles is shown in Fig. 10, where for all specimens tested. In some cases, the final MOR MOR reduction is the mOr divided by the maximum is larger than the initial MOR. The increase in MOR has MOR and total crack length is the sum of all crack been attributed to an increase in the interfacial shear lengths within 2 mm of the notch tip. It is seen from the stress during long-duration cyclic loading [ 12]246 Y. Miyashita et al. / International Journal of Fatigue 24 (2002) 241–248 Fig. 7. Schematic illustrations of crack growth processes. materials, the variation in MOR, as has been previously suggested [10–12], was used in this study. The MOR was calculated from stress–strain hysteresis loops, which were recorded during fatigue tests. The MOR was taken to be the slope of the unloading curve between the maximum stress and 10% of the maximum stress. The variation of the MOR reduction and of the total crack length with increasing number of cycles is shown in Fig. 10, where MOR reduction is the MOR divided by the maximum MOR and total crack length is the sum of all crack lengths within 2 mm of the notch tip. It is seen from the figure that the MOR reduction decreases with increase in the total crack length. It is also noted that in some cases, the MOR increased with crack growth at low stress levels (Fig. 10(a)). This anomalous behavior was observed for all types of crack growth processes. Initial MOR, final MOR and maximum MOR are shown in Fig. 11. Values of the maximum MOR are larger than the initial MOR for all specimens tested. In some cases, the final MOR is larger than the initial MOR. The increase in MOR has been attributed to an increase in the interfacial shear stress during long-duration cyclic loading [12]