S45C調質材の腐食疲労挙動と応力変動の影響  [in Japanese] Corrosion Fatigue Behavior of Heat-Treated Carbon Steel under Two-Step Loading  [in Japanese]

For the estimation of fatigue damage of plain specimens under complex loading, it is important to study the effect of stress change through the behavior of a small crack, because the fatigue life of specimens is determined mainly by the growth life of a small crack. However, such studies performed in corrosion environments are very few. In this study, using 3% NaCl solution, corrosion fatigue tests of plain specimens were carried out under the constant-ampli-tude, low-to-high block loading and high-to-low block loading. The behavior of cracks was detected by the plastic replica method. The cumulative cycle ratio Σ(N/N_f)was calculated for the variable-amplitude loading tests. The values of Σ(N/N_f)for high-to-low loading were smaller than unity, whereas they were neary unity for low-to-high loading. The difference in Σ(N/N_f)between two loading patterns can be explained based on the small crack propagation characteristics and the density of long cracks which led to fracture.