粗大結晶粒ニッケル合金の疲労き裂発生および進展挙動特性
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概要
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High cycle fatigue tests and computational studies of a coarse-grained Ni alloy were carried out to investigate fatigue crack nucleation and propagation behavior. Fatigue tests of a rectangular sample were performed by four-point bending under load control. Several interruptions were made to observe fatigue crack nucleation and propagations in the gauge region. Grain distribution and orientation of the tensile surface were characterized using electron beam backscattering diffraction pattern (EBSP) technique. A size of characterizing area was determined to sufficiently cover the inner span of four-point bending. Polycrystalline finite element analysis was made to investigate stress distributions of the specimen. Stresses were computed in global axis, such as longitudinal stress, and local axis, such as resolved shear stresses in slip systems, for whole grains. Longitudinal stress distributions tend to be affected by inter-grain relationships. Fatigue crack initiations tend to be occurred in areas indicating relatively high resolved shear stresses in slip systems.