STP1060: Evaluation of Finite-Element Models and Stress-Intensity Factors for Surface Cracks Emanating from Stress Concentrations

    Tan, PW
    Research scientist, senior scientist, and senior scientist, Analytical Services and Materials, Inc., Hampton, VA

    Raju, IS
    Research scientist, senior scientist, and senior scientist, Analytical Services and Materials, Inc., Hampton, VA

    Shivakumar, KN
    Research scientist, senior scientist, and senior scientist, Analytical Services and Materials, Inc., Hampton, VA

    Newman, JC
    Senior scientist, NASA Langley Research Center, Hampton, VA

    Pages: 15    Published: Jan 1990


    Abstract

    This paper presents an evaluation of the three-dimensional finite-element models and methods used to analyze surface cracks at stress concentrations. Previous finite-element models used by Raju and Newman for surface and corner cracks at holes were shown to have “ill-shaped” elements at the intersection of the hole and crack boundaries. These ill-shaped elements tended to make the model too stiff and, hence, gave lower stress-intensity factors near the hole-crack intersection than models without these elements. Improved models, without these ill-shaped elements, were developed for a surface crack at a circular hole and at a semicircular edge notch. Stress-intensity factors were calculated by both the nodal-force and virtual-crack-closure methods. Both methods and different models gave essentially the same results. Comparisons made between the previously developed stress-intensity factor equations and the results from the improved models agreed well except for configurations with large notch-radii-to-plate-thickness ratios.

    Stress-intensity factors for a semi-elliptical surface crack located at the center of a semicircular edge notch in a plate subjected to remote tensile loadings were calculated using the improved models. A wide range in configuration parameters was considered. The ratio of crack depth to crack length ranged from 0.4 to 2; of crack depth to plate thickness from 0.2 to 0.8; and of notch radius to plate thickness from 1 to 3. The finite-element or nonsingular elements models employed in the parametric study had singularity elements all along the crack front and linear-strain (eight-noded) elements elsewhere. The models had about 15 000 degrees of freedom. Stress-intensity factors were calculated by using the nodal-force or virtual-crack-closure method.

    Keywords:

    crack, surface cracks, crack propagation, fracture, stress analysis, fatigue (materials), stress-intensity factors, finite elements, boundary-layer region


    Paper ID: STP23425S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP23425S


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