STP942: Microstructural Aspects of Crack Initiation and Propagation in Extremely Low Cycle Fatigue

    Kunio, T
    Keio University, Yokohama,

    Shimizu, M
    Keio University, Yokohama,

    Ohtani, N
    Keio University, Yokohama,

    Abe, T
    Technical Research Center, Nippon Kokan K. K., Kawasaki,

    Pages: 14    Published: Jan 1988


    Abstract

    A study has been made of the crack initiation and propagation in a low cycle fatigue of annealed carbon steel including extremely short fatigue life (Nf < 100), with an emphasis on the establishment of the relation between the microfracture behavior and the damage accumulation process depending on the plastic strain range, Δεp, as well as the mean strain, εm.

    It was found that at the small Δεp the surface damage due to the initiation and propagation of surface microcracks is predominant, while at the very large Δεp giving fatigue life less than Nf = 10, the internal cracking originated from the fracture of a pearlite becomes a primary source of the damage which results in the reduction of the residual ductility, εFR. The transition from the surface damage to the internal one takes place when Δεp becomes so large that the pearlite cracking may start inside the material at each level of εm.

    Good correlation was obtained between the reduction of residual ductility and the cracked pearlite ratio newly defined as a parameter for the evaluation of the internal microfracture behavior.

    Keywords:

    low cycle fatigue, microfracture process, damage accumulation, surface crack, internal crack, residual ductility, mean strain, pearlite cracking


    Paper ID: STP24519S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP24519S


    CrossRef ASTM International is a member of CrossRef.