STP1343

    Role of Fatigue Crack Closure Stresses in Hydrogen-Assisted Cracking

    Published: Jan 1999


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    Abstract

    Crack closure effects on hydrogen-assisted cracking (HAC) were studied in terms of the influence of residual stresses produced by load removals at fatigue cycling on stress-assisted hydrogen diffusion towards rupture sites in the crack tip zone. The finite element procedure was applied to cyclic load elastoplastic large-deformation analysis combined with stress-assisted diffusion. Small-scale yielding near the crack tip was addressed and characterized in terms of the stress intensity factor (SIF). The elastoplastic situation near the tip of a blunting-closing crack revealed the cyclically stable stress evolution established after a couple of loading cycles (but this was not attained for strains). Crack closure effects were negligible for sustained-load HAC at SIF above the maximum value at precracking. The test duration for reliable evaluation of the threshold SIF for HAC was estimated. Crack closure affects near-tip hydrogen diffusion, and consequently HAC, at dynamic rising loading after precracking. Modeling was performed for the range of SIF increase rates. It showed that a premature fulfillment of the local fracture criterion in terms of critical combination of the hydrogen concentration and stress-strain parameters can occur at slow dynamic loading if compared with the sustained-load case. The dominating factor—stress or strain—and the “scale” of the local rupture event are of decisive importance for this. The performed simulations provide more insight into the items of conservatism of HAC testing data and the sources of their uncertainty.

    Keywords:

    hydrogen-assisted cracking, large crack-tip deformations, cyclic loading, stress-assisted diffusion, threshold stress intensity factor


    Author Information:

    Toribio, J
    University of La Coruña, E.T.S.I. Caminos, Campus de Elviña, La Coruña,

    Kharin, V
    University of La Coruña, E.T.S.I. Caminos, Campus de Elviña, La Coruña,

    Pidstryhach Institute for Applied Problems of Mechanics and Mathematics, Lviv,


    Paper ID: STP15773S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP15773S


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