Corrosion fatigue behavior of heat treated carbon steel under two step loading
Goto Masahiro; Nakajima Ken; Yakushiji Terutoshi; Nisitani Hironobu; Kawagoishi Norio; Miyagawa Hiroomi
Abstract: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 amplitude, 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 S(N/Nf) was calculated for the variable amplitude loading tests. The values of S(N/Nf) for high-to-low loading were smaller than unity, whereas they were nearly unity for low-to-high loading. The difference in S(N/Nf) between two loading patterns can be explained based on the small crack propagation characteristics and the density of long cracks which led to fracture. Key Words:corrosion fatigue, two-step loading, cumulative cycle ratio, small crack, plain specimen, heat-treated carbon steel