An Evaluation Technique for Fatigue Life of Multiple Surface Cracks

Abstract

This paper discusses an evaluation technique for fatigue life of multiple parallel surface cracks at one sided surface of a plate under axial and out-of-plate bending loads.This technique is a revision of the technique for multiple series surface cracks proposed in the previous paper, taking into account the experimentally-determined coalescence condition. If the initial ratio of the vertical distance H to the horizontal distance S between parallel surface cracks is 0.5 or less, or if H is 5 mm or less, these cracks propagate to unite substantially. In addition, there is no mutual influence between parallel surface cracks before coalescence in the virtual projected plane. After coalescence, these cracks propagate outside as a single crack. The fatigue crack in-going rate drops abruptly, in comparison with the out-going rate.As a result of case studies, it was found that the present technique can give us reasonable estimated fatigue life to coalescence and penetration.