Reduction of Stress Concentration at Edge of Stop Hole by Closing Crack Surface

概要

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In this paper, one technique for reduction of stress concentration at stop hole edges by closing the crack surface between stop holes using ICR treatment was proposed. Tensile and bending test results showed the effectiveness of reduction of stress concentration until opening the closed crack. In tensile test, closed crack opened after nominal stress of 100MPa, while closed crack did not open under nominal stress of 200MPa in bending test. Finite element analysis results also showed that the stress at crack closed by ICR treatment under tensile load was higher than that under bending moment. By closing the crack surface in both sides, the second moment of inertia is recovered about 70% of that without crack. On the other hand, the cross-section area closed by ICR treatment becomes one third of that without crack. Therefore, the nominal stress when the closed crack open under bending moment was higher than that under tensile load. Additionally, it was found that the stresses at closed crack under tensile load and bending moment were higher than that estimated stress by structural mechanics. The reason of this is that the stresses in closed crack area and in ligament areas are not sufficiently distributed. In this research, to estimate the stresses introduced at closed crack under tensile load and bending moment, simple equations considering the bias of stress distribution were also proposed.