Two-Step Multiple Block Loading Tests for a High Strength Steel Considering the Transition of Failure Mode in High Cycle Regime

Abstract

Fatigue behavior under variable amplitude loading was studied on a high carbon chromium steel, JIS SUJ2. Special attentions were paid on the evaluation of fatigue damage by the Palmgren-Miner rule and the damage mechanisms under variable amplitude loading accompanied by the failure mode transition in high cycle regime. Tests were performed using cantilever-type rotating bending fatigue testing machines in laboratory air. Load sequences employed were two-step multiple block loadings (low ↔ high). When two stress levels, under each of which the failure mode was the same, were applied, the failure mode was subsurface-type. Fatigue damages were evaluated successfully by the Palmgren-Miner rule. On the contrary, when the failure modes under both stress levels were different, the failure mode was surface-type. In this case, the cumulative damage at each stress level was independent of each other. Based on SEM observation, the morphologies of fish-eye formed under two-step multiple block loadings were the same as those under constant amplitude loadings.