圧縮残留応力場から伝播する疲労き裂の開閉口挙動に関する解析的検討

概要

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Initial residual stress due to welding was produced by thermo-elasto-plastic analysis based on F.E.M. calculation, thereafter cyclic-elasto-plastic analysis for fatigue crack propagation was carried out. A crack was propagated by 0.2 mm per one load cycle from compressive residual stress field to tensile stress field (stress ratio was 0.0). Crack opening and closing behavior was investigated in relation to re-distribution of residual stress and change of plastic region. Main results obtained are summarized as follows : 1. When the crack tip was in the stationary compressive residual stress field, as crack planes were kept in contact, the re-distribution of residual stress did not occur so much at unloading state. The crack opening was occurred at the crack root then moved to the crack tip, and this was also recognized in base metal analysis. 2. As the crack approached the initial tensile residual stress field, the residual stress re-distributed and the crack-opened-region remained near the crack tip even at unloading. The crack opening points were moved both to crack tip side and crack root side, and the crack tip opening occurred earlier than the full crack opening. 3. It was clarified that crack opening stress level would be able to be determined by strain gages glued just behind the crack tip, and using superposition model, the stress level could be estimated from the compressive residual stress distribution on the crack plane.
1987-05-05