Fatigue Crack Initiation and Propagation Behavior of a Nickel Alloy ; A Study of Structural Integrity Assessment Method Based on Polycrystalline FE Analysis
Shinya MIYAZAKI and Hidenari BABA
Abstract:Evaluation of fatigue crack nucleation and propagation behavior in anisotropic metals is necessary for improving an accuracy of structural integrity assessment. In this paper, high cycle fatigue tests and polycrystalline FE analyses were carried out to investigate a relationship between crack nucleation positions and stress distribution. Fatigue tests of a rectangular specimen were conducted by four-point bending under load control. Fatigue crack nucleation and propagation in the gauge region was carefully observed during the tests. Grain morphology and crystallographic orientation of tensile surface were characterized using electron beam backscattering diffraction pattern (EBSP) analysis. The size of characterized area was determined to sufficiently cover the gauge region of four-point bending inner span. Stress distribution of the specimen was computed by polycrystalline finite element analysis. Resolved shear stresses were calculated in expected twelve slip systems. Fatigue cracks were tend to be initiated in areas indicating relatively high resolved shear stresses in several slip systems. Key Words:Directionally solidified, Bending, Fatigue, Face centered cubic, Electron backscattering diffraction pattern, Polycrystalline finite element analysis