Published October 2012 | Version v1
Journal article

Damage assessment of low-cycle fatigue by crack growth prediction. Development of growth prediction model and its application

  • 1. Inst. of Nuclear Safety System, Inc., Inst. of Nuclear Technology, Mihama, Fukui (Japan)

Description

In this study, the fatigue damage was assumed to be equivalent to the crack initiation and its growth, and fatigue life was assessed by predicting the crack growth. First, a low-cycle fatigue test was conducted in air at room temperature under constant cyclic strain range of 1.2%. The crack initiation and change in crack size during the test were examined by replica investigation. It was found that a crack of 41.2 μm length was initiated almost at the beginning of the test, which was approximately at 9% of the total fatigue life. Therefore, the fatigue life was almost equivalent to the number of cycles necessary for crack growth to the critical size. The identified crack growth rate was shown to correlate well with the strain intensity factor, whose physical meaning was discussed in this study. The fatigue life prediction model (equation) under constant strain range was derived by integrating the crack growth equation defined using the strain intensity factor, and the predicted fatigue lives were almost identical to those obtained by low-cycle fatigue tests. The change in crack depth predicted by the equation also agreed well with the experimental results. Based on the crack growth prediction model, it was shown that the crack size would be less than 0.1 mm even when the estimated fatigue damage exceeded the critical value of the design fatigue curve, in which a twenty-fold safety margin was used for the assessment. It was revealed that the effect of component size and surface roughness, which have been investigated empirically by fatigue tests, could be reasonably explained by considering the crack initiation and growth. Furthermore, the environmental effect on the fatigue life was shown to be brought about by the acceleration of crack growth. It was concluded that the magnitude of the environmental effect on fatigue life could be estimated from the crack growth experiments. (author)

Additional details

Publishing Information

Journal Title
INSS Journal
Journal Volume
19
Journal Page Range
p. 166-182
ISSN
1340-4482

Optional Information

Notes
72 refs., 16 figs., 2 tabs.