Fracture and fatigue behavior of sintered steel at elevated temperatures: Part II. Fatigue crack propagation

Fatigue cracking resistance of sintered steel as a function of temperature is characterized by crack growth rate Its the stress intensity range, Delta K. The stress ratio effects on fatigue crack propagation (FCP) are investigated from room temperature to 300 degrees C. The crack closure effects on FCP are evaluated by both theoretical and experimental approaches. We found that the crack closure cannot be fully responsible for the observed increase of fatigue resistance with low stress ratio. Experimental results support that both K-max and Delta K control near-threshold crack growth. Fatigue crack resistance at high Delta K regime decreases with temperature. The apparent increase of fatigue resistance at the near-threshold regime at elevated temperatures might be attributed to microcrack toughening.