14. An Evaluation Technique for Fatigue Life of Multiple Surface Cracks

概要

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An evaluation technique for fatigue life of co-linear and parallel surface cracks at one sided surface of a plate under axial and out-of-plane bending loads was discussed in detail. If the initial ratio of the lateral distance H to the inside distance S between parallel surface cracks is 0.5 or less, or if H is 5 mm or less, these cracks can be considered to propagate to unite substancially from the experimental and theoretical investigation results. 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. Then, the rational method of estimating of fatigue life of multiple surface cracks to coalescence and penetration was proposed, taking this coalescence condition into consideration. As a result of case studies, it was confirmed that the present method can give more reasonable fatigue life to coalescence and penetration in comparison with the ASME Code Section XI. The accuracy of the present method was proved to be good by statistical analysis.
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