STP1189: Effect of Fiber-Matrix Debonding on Notched Strength of Titanium Metal-Matrix Composites

    Bigelow, CA
    Research engineer and senior scientist, NASA Langley Research Center, Hampton, VA

    Johnson, WS
    Research engineer and senior scientist, NASA Langley Research Center, Hampton, VA

    Pages: 17    Published: Jan 1993


    Abstract

    Two specimen configurations of a [0/90]2s SCS-6/Ti-15-3 laminate were tested and analyzed: a center-hole (CH) specimen and a double-edge-notched (DEN) specimen. The two specimen configurations failed at similar stress levels in spite of the large difference in the stress concentration factors for the two geometries. Microscopic examinations of the failure surfaces indicated more fiber-matrix debonding at the notch tip in the DEN specimen than in the CH specimen. Based on the experimental results, it was hypothesized that the radial stresses that developed at the fiber-matrix interface ahead of the notch tip in the DEN specimen caused fiber-matrix debonding in the 0° plies, thus lowering the stress concentration in the DEN specimen to a level comparable to that of the CH specimen.

    Two analytical techniques, a three-dimensional finite-element analysis and a macro-micro-mechanical analysis, were used to predict the overall stress-deformation behavior and the notch-tip fiber-matrix interface stresses in both configurations. The micromechanical analysis predicted radial stresses next to the notch in the DEN configuration that were nearly seven times as large as those predicted for the CH configuration. The overall stress-deformation response of both configurations was predicted accurately when debonding of the 90° plies was included. Predictions of the axial stress in the notch-tip 0° fiber correlated well with the specimen static strength when fiber-matrix debonding of 0° plies was included for the DEN specimen. The results shown indicate that a first fiber failure criteria based on the axial stress in the first intact 0° fiber can predict the static strength of notched specimens when interfacial damage is modeled.

    Keywords:

    micrographs, fracture mechanics, finite element analysis, micromechanics, fiber stress, fatigue (materials)


    Paper ID: STP24297S

    Committee/Subcommittee: E08.09

    DOI: 10.1520/STP24297S


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