Ni基単結晶超合金製十字型試験片による軸力－軸力組合せ負荷での多軸低サイクル疲労寿命評価

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This paper describes the multiaxial low cycle fatigue life of cruciform specimen of YH61 Ni base single crystal superalloy at high temperature. Biaxial tension-compression low cycle fatigue tests were performed using the cruciform specimen at 1173K under y-directional strain amplitude (εy) constant condition with varying x-directional strain amplitude (εx). Low cycle fatigue lives were influenced by the strain biaxiality and the maximum lives were obtained at εx/εy being equal to 0.5. The maximum principal strain and Mises equivalent strain ranges gave a large scatter in the correlation of the multiaxial low cycle fatigue lives. The principal stress and Mises equivalent stress ranges showed far better correlation than the strain ranges. Cracking mode was also discussed by observing the fracture surface at failure. Cracks propagated in the 45 degree direction to x direction at εx/εy = -1 test while those in the x direction in the other cases. Cracks were initiated at the life ratio less than 0.2 at Ni3(Al+Ta) eutectic alloy part and propagated with cycles.