STP1203: Tensile and Tension-Tension Fatigue Fracture Behavior of γ-Al2O3/Al Metal Matrix Composite at Room and Elevated Temperature

    Komai, K
    Professor and Associate Professor, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto,

    Minoshima, K
    Professor and Associate Professor, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto,

    Funato, T
    Graduate student, Graduate School of Engineering, Kyoto UniversityMitsubishi Heavy Industries, Yoshida-Honmachi, Sakyo-ku, KyotoNagoya,

    Pages: 26    Published: Jan 1993


    Abstract

    Tensile and tension-tension fatigue (stress ratio: 0.05) fracture behavior of a continuous γ-Al2O3 fiber reinforced aluminum (Al-0.5Ba) matrix metal matrix composite (fiber volume fraction: 50%) manufactured by a squeeze casting process was investigated in laboratory air at room and elevated temperature (573 K). Special attention was paid to fracture processes: in situ observation of static fracture processes was also made in a scanning electron microscope (SEM). Fracture surfaces were closely examined with an SEM, and we have discussed the tensile and fatigue fracture mechanisms. The fiber reinforcement improved the material properties, including tensile strength, elastic modulus and fatigue strength of both [0°], [0°/90°], and [ ±45°] composites, compared with those of unreinforced equivalent matrix materials, 1XXX series aluminums. The in situ observation in the SEM showed that the static fracture of [0°] and [0°/90°] composites was controlled by failures of 0° plies, and the fracture initiated at broken fibers at the specimen surface. In the case of [±45°] composites, intralaminar failures at the middle position in thickness occurred, leading to interlaminar deformation and failures, and finally unstable fracture. The tensile strength of [0°] composites at 573 K was higher than that at room temperature. In the case of [0°/90°] composites, there was little difference in strength between room temperature and 573 K. However, strength at 573 K of [ ± 45°] composites decreased from that at room temperature. Both at room temperature and at 573 K, few fiber pullouts were observed and pullout fibers were covered with matrix. Failures of [90°] composites occurred in matrix near fiber/matrix interfaces and fiber splitting also existed. These indicated that the composite had excellent fiber/matrix interfacial strength. Failure mechanisms of fatigue in [0°] composites differed depending on stress level; at high stress levels, final failures were brought about by a macroscopic transverse crack, whereas at low stress levels, longitudinal crack first initiated and propagated in the longitudinal direction, that is, loading axis direction. This longitudinal crack reached the gripped position, and then a macroscopic transverse crack was initiated and propagated, resulting in final failure. In the case of [±45°] composites, macroscopic failures occurred in the transverse direction, irrespective of stress level, and the S-N curve was very flat.

    Keywords:

    metal matrix composite, fracture, tensile test, tension-tension fatigue, fatigue strength, fracture surface, in situ observation, scanning electron microscope, elevated temperature, continuous fiber, alumina fiber, aluminum matrix


    Paper ID: STP14904S

    Committee/Subcommittee: D30.07

    DOI: 10.1520/STP14904S


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