微小試験片を用いた鉄単結晶のせん断疲労特性評価

抄録

In this study, shear fatigue limits of iron single crystals were evaluated by small specimens (cross-sectional dimensions: 0.5 × 0.15 mm). The specimens were small enough to be prepared from the iron single crystals, aiming at shear loadings for <111> slip directions on specific {110} and {123} planes. Using these specimens, shear fatigue tests were conducted for {110}<111> and {123}<111> slip systems. The shear fatigue limit for the {110} slip system was 115 MPa, whereas that for the {123} slip system was 135 MPa. Then, the shear fatigue limit for the {123} slip system was 1.2 times of that for the {110} slip system. The specimens for both slip systems were fractured on the plane substantially perpendicular to the axial direction. Slopes between width direction and the fractured surfaces for the {110} and {123} slip planes were 0.0° and 1.3°, respectively. As the slopes were sufficiently small, the entire fracture surfaces were mainly caused by the activation of a primary slip system. The fracture surfaces of both slip systems at the maximum shear stress part were flat with parallel lines for slip direction. Although the entire fracture surfaces were slightly different, these results imply that the fracture surfaces at the maximum shear stress part were attributable to the activation of the primary slip system. Thus, the fatigue limits evaluated by the small specimens would represent fatigue strengths for the {110}<111> and {123}<111> slip systems, respectively.