STP1330

    Effect of Stress and Geometry on Fatigue Crack Growth Perpendicular to Fibers in Ti-6Al-4V Reinforced with Unidirectional SiC Fibers

    Published: Jan 1998


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    Abstract

    Critical turbine engine and aircraft components fabricated from continuous fiber-reinforced metal matrix composite (MMC) will experience cyclic loads during service, and many of these components typically contain crack initiators. Hence, extensive characterization of the fatigue crack growth behavior of a model MMC ([0]8 SCS-6/Ti-6Al-4V) was initiated by the USAF Wright Laboratory. This paper discusses some of the results of the experimental and analytical investigation of fatigue crack propagation in [0]8 SCS-6/Ti-6Al-4V. Automated fatigue crack growth tests were conducted using middle tension, M(T), specimens at 23°C with a stress ratio of 0.1. During some of the tests, the crack opening displacement profile was measured to verify the stress distributions predicted by fiber-bridging models. The results are also compared with those available for SM1240/Ti-6Al-4V under tension and bending fatigue loading. This study showed that the shear lag model assuming a constant value of τ can be used to predict bridged crack growth perpendicular to fibers in SCS-6/Ti-6Al-4V and SM1240/Ti-6Al-4V over a wide range of stress levels and under tension and bending fatigue loading conditions. The predictions of partially bridged and unbridged crack growth, crack opening displacements, and slip lengths correlated well with the data. The value of the fiber/matrix interfacial shear stress, τ, was the same for SCS-6/Ti-6Al-4V and SM1240/Ti-6Al-4V, implying that the bridging mechanism of the SMI240 fiber is identical to that of the SCS-6 fiber at room temperature. The results also indicate that the onset of fiber failure could be predicted using the bundle strength as the critical value.

    Keywords:

    bridging stress-intensity factor, center crack, crack growth rate, crack opening displacement, cyclic loading, fatigue crack growth, fiber bridging, life prediction, metal matrix composite, shear lag model, titanium matrix composite


    Author Information:

    John, R
    Materials and Manufacturing Directorate, Air Force Research Laboratory (AFRL/MLLN)University of Dayton Research Institute, Wright Patterson Air Force BaseDayton, OHOH

    Jira, JR
    Materials and Manufacturing Directorate, Air Force Research Laboratory (AFRL/MLLN)University of Dayton Research Institute, Wright Patterson Air Force BaseDayton, OHOH

    Larsen, JM
    Materials and Manufacturing Directorate, Air Force Research Laboratory (AFRL/MLLN)University of Dayton Research Institute, Wright Patterson Air Force BaseDayton, OHOH


    Paper ID: STP13269S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP13269S


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