The role of strain ratcheting and mesh refinement in finite element analyses of plasticity induced crack closure

Kristine B. Cochran, Robert H. Dodds, Keith Hjelmstad

    Research output: Contribution to journalArticle

    25 Citations (Scopus)

    Abstract

    Numerical investigations of plasticity induced crack closure using the finite element method typically assume: (1) the opening behavior remains independent of the simulated rate of crack growth, and (2) a threshold element size exists below which crack opening loads become mesh independent. Nevertheless, examples in the recent literature and also in the present work indicate these assumptions do not always hold. The current work demonstrates the field results (displacements, stress-strain) for cyclic loading of stationary cracks converge with mesh refinement. However, when the cyclic load regime includes systematic crack extension, certain conditions lead to highly mesh dependent fields and opening loads. The cyclic accumulation of permanent deformation (strain ratcheting) necessarily produces mesh dependence when the finite element size dictates the rate of crack growth. Moreover, extensive ratcheting leads to physically unrealistic shapes of the crack opening profiles. This work explores the link between strain ratcheting, mesh dependence and load-cycle effects within a small-scale yielding framework, including the influence of plane strain vs. plane stress constraints, constitutive definition (non-hardening, linear kinematic hardening and nonlinear kinematic hardening) and the monotonic flow properties. Key conclusions from this work include: (1) near-tip strain ratcheting generally increases with decreased hardening and can be much more pronounced in plane strain than in plane stress; (2) for models with significant ratcheting, slower rates of simulated growth due to smaller element size and/or more load cycles between crack advancements generally reduce the opening loads; and (3) the computed opening loads depend intrinsically on the amount of ratcheting, and the rate of crack growth as determined by the element size and number of load cycles between crack advancements.

    Original languageEnglish (US)
    Pages (from-to)1205-1220
    Number of pages16
    JournalInternational Journal of Fatigue
    Volume33
    Issue number9
    DOIs
    StatePublished - Sep 2011

    Fingerprint

    Crack Closure
    Crack closure
    Mesh Refinement
    Plasticity
    Finite Element
    Cracks
    Crack
    Hardening
    Crack propagation
    Crack Growth
    Mesh
    Plane Stress
    Loads (forces)
    Plane Strain
    Kinematics
    Threshold elements
    Cycle
    Cyclic loads
    Stress Constraints
    Cyclic Loading

    Keywords

    • Crack closure
    • Cycle dependence
    • Finite element analysis
    • Mesh dependence
    • Nonlinear plasticity
    • Small-scale yielding

    ASJC Scopus subject areas

    • Industrial and Manufacturing Engineering
    • Mechanical Engineering
    • Mechanics of Materials
    • Materials Science(all)
    • Modeling and Simulation

    Cite this

    The role of strain ratcheting and mesh refinement in finite element analyses of plasticity induced crack closure. / Cochran, Kristine B.; Dodds, Robert H.; Hjelmstad, Keith.

    In: International Journal of Fatigue, Vol. 33, No. 9, 09.2011, p. 1205-1220.

    Research output: Contribution to journalArticle

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