Abstract
Many failure accidents have indicated fatigue as the primary cause for the failure of a machine or structure. In general, the origin of failure is a structural discontinuous part such as a welded joint or a notched member that causes stress concentration. While designing such a component, a finite element analysis (FEA) has to be conducted, and the peak stress has to be compared with a design fatigue curve obtained from small-sized specimens to evaluate whether the component satisfies the design life. However, it is known that a fatigue life prediction at a stress concentration part based on a peak stress always provides an excessively conservative estimation. This is due to the stress gradient of the component. This paper discusses the stress-gradient approach to eliminate the conservatism and rationalize a fatigue design. Using literature test data, the relationship between the stress gradient calculated using FEA, and the fatigue strength reduction ratio was determined. Later, a fatigue test was conducted on a notched specimen of low-alloy steel to verify the stress-gradient approach, and the fatigue life of the notched specimen was predicted considering the stress gradient at the notch root. The predicted fatigue life agreed well with the experimental results.
Fatigue life prediction of notched components: a comparison between the theory of critical distance and the classical stress-gradient approach
