STP580: Molecular Correlations with Fracture in Fibers and Granular-Filled Composites

    DeVries, KL
    Professor of mechanical engineering, post-doctoral fellow, and research assistant, University of Utah, Salt Lake City, Utah

    Lloyd, BA
    Professor of mechanical engineering, post-doctoral fellow, and research assistant, University of Utah, Salt Lake City, Utah

    Wilde, TB
    Professor of mechanical engineering, post-doctoral fellow, and research assistant, University of Utah, Salt Lake City, Utah

    Pages: 17    Published: Jan 1975


    Abstract

    Failure in polymeric materials might be envisioned as occurring by any of several molecular mechanisms. Where homolytic bond rupture occurs, free radicals (unpaired electrons) result. This paper presents results of electron spin resonance studies of chain-scission kinetics in (1) oriented nylon fibers and (2) in granular-filled elastomer composites.

    The most extensive work to date has been done on high-strength oriented fibers. It has been concluded that many of the desirable properties of fibers can be attributed to their own microscopic physical composite nature. A reaction-rate molecular model is proposed and is successfully used as a failure criterion to predict failure under various loadings.

    The model assumes a statistical distribution in stress on the polymeric chain structure. Failure first occurs in the more highly stressed regions with a subsequent redistribution of the load among the unfractured elements in the fiber. Once the physical parameters are determined for a given material, behavior for other loading is predicted by numerical techniques. Electron spin resonance was used also to investigate interfacial failure in filled composites. Depending on the magnitude of the interactive forces, failure at the interface between the filler and the matrix may be largely adhesive (dewetting) or cohesive in nature. In the former case little or no detectable bond rupture occurs while in the latter case significant free radical concentrations may be produced. Electron spin resonance and scanning electron microscopy are used to systematically investigate the role of the surface interaction, dewetting, etc. on the strength and toughness of composites.

    Keywords:

    composite materials, fibers, elastomers, polymers, failure, nylon fibers, bonding strength, toughness


    Paper ID: STP32327S

    Committee/Subcommittee: D30.05

    DOI: 10.1520/STP32327S


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