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    Fatigue Fracture Micromechanisms in Poly(Methyl Methacrylate) of Broad Molecular Weight Distribution

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    Scanning electron microscopy was used to examine the fatigue fracture surfaces of poly(methyl methacrylate) of varying molecular weight (MW) and molecular weight distribution. The specimens had been synthesized to incorporate various porportions of high- and low-MW tails in high, medium, and low-MW matrixes. In specimens with a high-MW matrix, increased proportions of low-MW additions resulted in higher fatigue crack growth rates and a gradual shift in the appearance of the fracture surface toward that of a low-MW matrix specimen with a small addition of a high-MW specie. Crack advance was continuous, with fatigue striation widths corresponding to the macroscopically measured growth increment associated with each loading cycle. In low-MW matrixes, addition of medium- and high-MW species resulted in attenuated crack growth rates and resulting longer life. With less than 2 percent of the medium- and high-MW species, crack advance was by a discontinuous mode with each growth increment equal to the size of the plastic zone at the crack tip. At high ΔK levels, discontinuous growth bands took on a scalloped appearance while maintaining a second power dependence between bandwidth and ΔK.


    poly(methyl methacrylate), fatigue crack propagation, fatigue striations, discontinuous growth bands, polymer fatigue, fracture mechanics, fractography

    Author Information:

    Janiszewski, J
    Metallurgical consultant, Mohnton, Pa.

    Hertzberg, RW
    Professors of metallurgy and chemistry, Lehigh University, Bethlehem, Pa.

    Manson, JA
    Professors of metallurgy and chemistry, Lehigh University, Bethlehem, Pa.

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP28794S