Volume 5, Issue 8 (September 2008)

    Elastic-Plastic Finite-Element Analyses of Compression Precracking and Its Influence on Subsequent Fatigue-Crack Growth

    (Received 5 December 2007; accepted 7 July 2008)

    Published Online: 2008

    CODEN: JAIOAD

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    Abstract

    Compression precracking has been used in a renewed effort to generate fatigue-crack growth rates in the threshold and near-threshold regimes, as an alternative to the traditional load-reduction procedure. But concerns have been expressed on the influence of tensile residual stresses resulting from compressive yielding at the crack-starter notch. This paper uses elastic-plastic, finite-element analyses to study the influence of the tensile residual stresses induced by compression precracking on simulated crack growth under constant-amplitude loading. High-fidelity finite-element models (60 000 to 160 000 DOF) using two-dimensional plane-stress analyses were used to model plastic yielding during compressive loading and simulated fatigue-crack growth through the tensile residual-stress field. The finite-element code was ZIP2D and the course mesh had an element size of 2 μm. A refined mesh had an element size four times smaller (0.5 μm) than the course mesh. Fatigue-crack growth and crack-closure effects were simulated over a wide range in stress ratios (R=0 to 0.8) and load levels, after compression precracking. The crack-tip-opening displacement (CTOD) concept was used to judge the extent of the influence on the tensile residual stresses and the stabilization of the crack-opening loads. It was found that the tensile residual stress field decayed as the crack grew under cyclic loading. Once the crack had reached one compressive plastic-zone size, the tensile residual-stress field had dissipated. However, the stabilization of the crack-opening loads and merging of the CTOD values with and without compression precracking was found to be about 1.5 to 2 times the compressive plastic-zone size at R=0 loading. The effects dissipated at smaller distances from the notch tip for the higher stress ratios. The present results have validated the crack-extension criterion that had been proposed for use in the compressive precracking threshold test method, beyond which, cracks are growing under constant-amplitude (steady-state) behavior.


    Author Information:

    Yamada, Y.
    Department of Aerospace Engineering, Mississippi State University, Mississippi State, MS

    Newman, J. C.
    Department of Aerospace Engineering, Mississippi State University, Mississippi State, MS

    Department of Aerospace Engineering, Mississippi State University, Mississippi State, MS


    Stock #: JAI101617

    ISSN: 1546-962X

    DOI: 10.1520/JAI101617

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    Author
    Title Elastic-Plastic Finite-Element Analyses of Compression Precracking and Its Influence on Subsequent Fatigue-Crack Growth
    Symposium Seventh International ASTM/ESIS Symposium on Fatigue and Fracture Mechanics (36th ASTM National Symposium on Fatigue and Fracture Mechanics), 2007-11-16
    Committee E08